Mobile communication system

ABSTRACT

A mobile communication system hybridly allows, in a case where an access group consisting of one or more user equipments and one or more base stations is registered, the base station included in the access group to have access in a closed mode from the user equipment included in the same access group and access in an open mode from a user equipment that is not included in the same access group, wherein a communication area of the base station in the open mode is identical to a communication area of the base station in the closed mode. This eliminates a communication area in which the base station serving as an access destination differs between the user equipment in the closed mode and the user equipment in the open mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/499,737 filed Apr. 2, 2012, which is a National Phase ofPCT/JP2010/005625 filed Sep. 15, 2010, and claims priority to JapanesePatent Application No. 2009-230548 filed Oct. 2, 2009. The entirecontents of each of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a mobile communication system in whicha base station performs radio communication with a plurality of userequipments.

BACKGROUND ART

Commercial service of a wideband code division multiple access (W-CDMA)system among so-called third-generation communication systems has beenoffered in Japan since 2001. In addition, high speed down link packetaccess (HSDPA) service for achieving higher-speed data transmissionusing a down link has been offered by adding a channel for packettransmission high speed-downlink shared channel (HS-DSCH)) to the downlink (dedicated data channel, dedicated control channel). Further, inorder to increase the speed of data transmission in an uplink direction,service of a high speed up link packet access (HSUPA) has been offered.W-CDMA is a communication system defined by the 3rd generationpartnership project (3GPP) that is the standard organization regardingthe mobile communication system, where the specifications of Release 8version are produced.

Further, 3GPP is studying new communication systems referred to as “longterm evolution (LTE)” regarding radio areas and “system architectureevolution (SAE)” regarding the overall system configuration including acore network (merely referred to as network as well) as communicationsystems independent of W-CDMA. In the LTE, an access scheme, a radiochannel configuration and a protocol are totally different from those ofthe current W-CDMA (HSDPA/HSUPA). For example, as to the access scheme,code division multiple access is used in the W-CDMA, whereas in the LTE,orthogonal frequency division multiplexing (OFDM) is used in a downlinkdirection and single career frequency division multiple access (SC-FDMA)is used in an uplink direction. In addition, the bandwidth is 5 MHz inthe W-CDMA, while in the LTE, the bandwidth can be selected from 1.4MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz for each base station.Further, differently from the W-CDMA, circuit switching is not providedbut a packet communication system is only provided in the LTE.

The LTE is defined as a radio access network independent of the W-CDMAnetwork because its communication system is configured with a new corenetwork different from a core network (GPRS) of the W-CDMA. Therefore,for differentiation from the W-CDMA communication system, a base stationthat communicates with a user equipment (UE) and a radio networkcontroller that transmits/receives control data and user data to/from aplurality of base stations are referred to as an E-UTRAN NodeB (eNB) andan evolved packet core (EPC: also referred to as access gateway (aGW)),respectively, in the LTE communication system. Unicast service andevolved multimedia broadcast multicast service (E-MBMS service) areprovided in this LTE communication system. The E-MBMS service isbroadcast multimedia service, which is merely referred to as MBMS insome cases. Bulk broadcast contents such as news, weather forecast andmobile broadcast are transmitted to a plurality of UEs. This is alsoreferred to as point to multipoint service.

Non-Patent Document 1 describes the current decisions by 3GPP regardingan overall architecture in the LTE system. The overall architecture(Chapter 4.6.1 of Non-Patent Document 1) is described with reference toFIG. 1. FIG. 1 is a diagram illustrating the configuration of the LTEcommunication system. With reference to FIG. 1, the evolved universalterrestrial radio access (E-UTRAN) is composed of one or a plurality ofbase stations 102, provided that a control protocol (for example, radioresource management (RRC)) and a user plane (for example, packet dataconvergence protocol (PDCP), radio link control (RLC), medium accesscontrol (MAC), and physical layer (PHY)) for a UE 101 are terminated inthe base station 102. The base stations 102 perform scheduling andtransmission of paging signaling (also referred to as paging messages)notified from a mobility management entity (MME) 103. The base stations102 are connected to each other by means of an X2 interface. Inaddition, the base stations 102 are connected to an evolved packet core(EPC) by means of an S1 interface, more specifically, connected to themobility management entity (MME) 103 by means of an S1_MME interface andconnected to a serving gateway (S-GW) 104 by means of an S1_U interface.The MME 103 distributes the paging signaling to multiple or a singlebase station 102. In addition, the MME 103 performs mobility control ofan idle state. When the UE is in the idle state and an active state, theMME 103 manages a list of tracking areas. The S-GW 104transmits/receives user data to/from one or a plurality of base stations102. The S-GW 104 serves as a local mobility anchor point in handoverbetween base stations. Moreover, there is provided a PDN gateway (P-GW),which performs per-user packet filtering and UE-ID address allocation.

The control protocol RRC between the UE 101 and the base station 102performs broadcast, paging, RRC connection management and the like. Thestates of the base station and the UE in RRC are classified intoRRC_Idle and RRC_CONNECTED. In RRC_IDLE, public land mobile network(PLMN) selection, system information (SI) broadcast, paging, cellreselection, mobility and the like are performed. In RRC_CONNECTED, theUE has RRC connection, is capable of transmitting/receiving data to/froma network, and performs, for example, handover (HO) and measurement of aneighbor cell.

The current decisions by 3GPP regarding the frame configuration in theLTE system are described in Non-Patent Document 1 (Chapter 5), which aredescribed with reference to FIG. 2. FIG. 2 is a diagram illustrating theconfiguration of a radio frame used in the LTE communication system.With reference to FIG. 2, one radio frame is 10 ms. The radio frame isdivided into ten equally sized subframes. The subframe is divided intotwo equally sized slots. The first and sixth subframes contain adownlink synchronization signal (SS) per each radio frame. Thesynchronization signals are classified into a primary synchronizationsignal (P-SS) and a secondary synchronization signal (S-SS).Multiplexing of channels for multimedia broadcast multicast servicesingle frequency network (MBSFN) and for non-MBSFN is performed on aper-subframe basis. Hereinafter, a subframe for MBSFN transmission isreferred to as an MBSFN subframe. Non-Patent Document 2 describes asignaling example when MBSFN subframes are allocated. FIG. 3 is adiagram illustrating the configuration of the MBSFN frame. Withreference to FIG. 3, the MBSFN subframes are allocated for each MBSFNframe. An MBSFN frame cluster is scheduled. A repetition period of theMBSFN frame cluster is allocated.

Non-Patent Document 1 describes the current decisions by 3GPP regardingthe channel configuration in the LTE system. It is assumed that the samechannel configuration is used in a closed subscriber group (CSG) cell asthat of a non-CSG cell. A physical channel (Chapter 5 of Non-PatentDocument 1) is described with reference to FIG. 4. FIG. 4 is a diagramillustrating physical channels used in the LTE communication system.With reference to FIG. 4, a physical broadcast channel (PBCH) 401 is adownlink channel transmitted from the base station 102 to the UE 101. ABCH transport block is mapped to four subframes within a 40 ms interval.There is no explicit signaling indicating 40 ms timing. A physicalcontrol format indicator channel (PCFICH) 402 is transmitted from thebase station 102 to the UE 101. The PCFICH notifies the number of OFDMsymbols used for PDCCHs from the base station 102 to the UE 101. ThePCFICH is transmitted in each subframe. A physical downlink controlchannel (PDCCH) 403 is a downlink channel transmitted from the basestation 102 to the UE 101. The PDCCH notifies the resource allocation,HARQ information related to DL-SCH (downlink shared channel that is oneof the transport channels shown in FIG. 5) and the PCH (paging channelthat is one of the transport channels shown in FIG. 5). The PDCCHcarries an uplink scheduling grant. The PDCCH carries ACK/Nack that is aresponse signal to uplink transmission. The PDCCH is referred to as anL1/L2 control signal as well. A physical downlink shared channel (PDSCH)404 is a downlink channel transmitted from the base station 102 to theUE 101. A DL-SCH (downlink shared channel) that is a transport channeland a PCH that is a transport channel are mapped to the PDSCH. Aphysical multicast channel (PMCH) 405 is a downlink channel transmittedfrom the base station 102 to the UE 101. A multicast channel (MCH) thatis a transport channel is mapped to the PMCH.

A physical uplink control channel (PUCCH) 406 is an uplink channeltransmitted from the UE 101 to the base station 102. The PUCCH carriesACK/Nack that is a response signal to downlink transmission. The PUCCHcarries a channel quality indicator (CQI) report. The CQI is qualityinformation indicating the quality of received data or channel quality.In addition, the PUCCH carries a scheduling request (SR). A physicaluplink shared channel (PUSCH) 407 is an uplink channel transmitted fromthe UE 101 to the base station 102. A UL-SCH (uplink shared channel thatis one of the transport channels shown in FIG. 5) is mapped to thePUSCH. A physical hybrid ARQ indicator channel (PHICH) 408 is a downlinkchannel transmitted from the base station 102 to the UE 101. The PHICHcarries ACK/Nack that is a response to uplink transmission. A physicalrandom access channel (PRACH) 409 is an uplink channel transmitted fromthe UE 101 to the base station 102. The PRACH carries a random accesspreamble.

A downlink reference signal which is a known symbol in a mobilecommunication system is inserted in the first, third and last OFDMsymbols of each slot. The physical layer measurement objects of a UEinclude, for example, reference symbol received power (RSRP).

The transport channel (Chapter 5 of Non-Patent Document 1) is describedwith reference to FIG. 5. FIG. 5 is a diagram illustrating transportchannels used in the LTE communication system. Part [A] of FIG. 5 showsmapping between a downlink transport channel and a downlink physicalchannel. Part [B] of FIG. 5 shows mapping between an uplink transportchannel and an uplink physical channel. A broadcast channel (BCH) isbroadcast to the entire base station (cell) regarding the downlinktransport channel. The BCH is mapped to the physical broadcast channel(PBCH). Retransmission control according to a hybrid ARQ (HARM) isapplied to a downlink shared channel (DL-SCH). Broadcast to the entirebase station (cell) is enabled. The DL-SCH supports dynamic orsemi-static resource allocation. The semi-static resource allocation isalso referred to as persistent scheduling. The DL-SCH supportsdiscontinuous reception (DRX) of a UE for enabling the UE to save power.The DL-SCH is mapped to the physical downlink shared channel (PDSCH).The paging channel (PCH) supports DRX of the UE for enabling the UE tosave power. Broadcast to the entire base station (cell) is required. ThePCH is mapped to physical resources such as the physical downlink sharedchannel (PDSCH) that can be used dynamically for traffic or physicalresources such as the physical downlink control channel (PDCCH) of theother control channel. The multicast channel (MCH) is used for broadcastto the entire base station (cell). The MCH supports SFN combining ofMBMS service (MTCH and MCCH) in multi-cell transmission. The MCHsupports semi-static resource allocation. The MCH is mapped to the PMCH.

Retransmission control according to a hybrid ARQ (HARQ) is applied to anuplink shared channel (UL-SCH). The UL-SCH supports dynamic orsemi-static resource allocation. The UL-SCH is mapped to the physicaluplink shared channel (PUSCH). A random access channel (RACH) shown inpart [B] of FIG. 5 is limited to control information. There is acollision risk. The RACH is mapped to the physical random access channel(PRACH).

The HARQ is described. The HARQ is the technique for improving thecommunication quality of a channel by combination of automatic repeatrequest and forward error correction. The HARQ has an advantage thaterror correction functions effectively by retransmission even for achannel whose communication quality changes. In particular, it is alsopossible to achieve further quality improvement in retransmissionthrough combination of the reception results of the first transmissionand the reception results of the retransmission. An example of theretransmission method is described. In a case where the receiver failsto successfully decode the received data (in a case where a cyclicredundancy check (CRC) error occurs (CRC=NG)), the receiver transmits“Nack” to the transmitter. The transmitter that has received “Nack”retransmits the data. In a case where the receiver successfully decodesthe received data (in a case where a CRC error does not occur (CRC=OK)),the receiver transmits “AcK” to the transmitter. The transmitter thathas received “Ack” transmits the next data. Examples of the HARQ systeminclude “chase combining”. In chase combining, the same data sequence istransmitted in the first transmission and retransmission, which is thesystem for improving gains by combining the data sequence of the firsttransmission and the data sequence of the retransmission inretransmission. This is based on the idea that correct data is partiallyincluded even if the data of the first transmission contains an error,and highly accurate data transmission is enabled by combining thecorrect portions of the first transmission data and the retransmissiondata. Another example of the HARQ system is incremental redundancy (IR).The IR is aimed to increase redundancy, where a parity bit istransmitted in retransmission to increase the redundancy by combiningthe first transmission and retransmission, to thereby improve thequality by an error correction function.

A logical channel (Chapter 6 of Non-Patent Document 1) is described withreference to FIG. 6. FIG. 6 is a diagram illustrating logical channelsused in an LTE communication system. Part [A] of FIG. 6 shows mappingbetween a downlink logical channel and a downlink transport channel.Part [B] of FIG. 6 shows mapping between an uplink logical channel andan uplink transport channel. A broadcast control channel (BCCH) is adownlink channel for broadcast system control information. The BCCH thatis a logical channel is mapped to the broadcast channel (BCH) ordownlink shared channel (DL-SCH) that is a transport channel. A pagingcontrol channel (PCCH) is a downlink channel for transmitting pagingsignals. The PCCH is used when the network does not know the celllocation of a UE. The PCCH that is a logical channel is mapped to thepaging channel (PCH) that is a transport channel. A common controlchannel (CCCH) is a channel for transmission control information betweenUEs and a base station. The CCCH is used in a case where the UEs have noRRC connection with the network. In downlink, the CCCH is mapped to thedownlink shared channel (DL-SCH) that is a transport channel. In uplink,the CCCH is mapped to the UL-SCH that is a transport channel.

A multicast control channel (MCCH) is a downlink channel forpoint-to-multipoint transmission. The MCCH is a channel used fortransmission of MBMS control information for one or several MTCHs from anetwork to a UE. The MCCH is a channel used only by a UE duringreception of the MBMS. The MCCH is mapped to the downlink shared channel(DL-SCH) or multicast channel (MCH) that is a transport channel. Adedicated control channel (DCCH) is a channel that transmits dedicatedcontrol information between a UE and a network. The DCCH is mapped tothe uplink shared channel (UL-SCH) in uplink and mapped to the downlinkshared channel (DL-SCH) in downlink. A dedicated traffic channel (DTCH)is a point-to-point communication channel for transmission of userinformation to a dedicated UE. The DTCH exists in uplink as well asdownlink. The DTCH is mapped to the uplink shared channel (UL-SCH) inuplink and mapped to the downlink shared channel (DL-SCH) in downlink. Amulticast traffic channel (MTCH) is a downlink channel for traffic datatransmission from a network to a UE. The MTCH is a channel used only bya UE during reception of the MBMS. The MTCH is mapped to the downlinkshared channel (DL-SCH) or multicast channel (MCH).

GCI represents a global cell identity. A closed subscriber group (CSG)cell is introduced in the LTE and universal mobile telecommunicationsystem (UMTS). The CSG is described below (Chapter 3.1 of Non-PatentDocument 3). The closed subscriber group (CSG) is a cell in whichsubscribers who are allowed to use are identified by an operator (cellfor identified subscribers). The identified subscribers are allowed toaccess one or more E-UTRAN cells of a public land mobile network (PLMN).One or more E-UTRAN cells in which the identified subscribers areallowed to access are referred to as “CSG cell(s)”. Note that access islimited in the PLMN. The CSG cell is part of the PLMN that broadcasts aspecific CSG identity (CSG ID, CSG-ID). The authorized members of thesubscriber group who have registered in advance access the CSG cellsusing the CSG-ID that is the access permission information. The CSG-IDis broadcast by the CSG cell or cells. A plurality of CSG-IDs exist in amobile communication system. The CSG-IDs are used by UEs for makingaccess from CSG-related members easier. The locations of UEs are tracedbased on an area composed of one or more cells. The locations are tracedfor enabling tracing of the locations of UEs and calling (calling ofUEs) even in an idle state. An area for tracing locations of UEs isreferred to as a tracking area. A CSG whitelist is a list stored in theUSIM in which all CSG IDs of the CSG cells to which the subscribersbelong are recorded. The CSG whitelist is also referred to as an allowedCSG ID list in some cases.

A “suitable cell” is described below (Chapter 4. 3 of Non-PatentDocument 3). The “suitable cell” is a cell on which a UE camps to obtainnormal service. Such a cell shall fulfill the following: (1) the cell ispart of the selected PLMN or the registered PLMN, or part of the PLMN ofan “equivalent PLMN list”; and (2) according to the latest informationprovided by a non-access stratum (NAS), the cell shall further fulfillthe following conditions: (a) the cell is not a barred cell; (b) thecell is part of at least one tracking area (TA), not part of “forbiddenLAs for roaming”, where the cell needs to fulfill (1) above; (c) thecell shall fulfill the cell selection criteria; and (d) for a cellidentified as CSG cell by system information (SI), the CSG-ID is part ofa “CSG whitelist” of the UE (contained in the CSG whitelist of the UE).

An “acceptable cell” is described below (Chapter 4.3 of Non-PatentDocument 3). This is the cell on which a UE camps to obtain limitedservice (emergency calls). Such a cell shall fulfill all the followingrequirements. That is, the minimum required set for initiating anemergency call in an E-UTRAN network are as follows: (1) the cell is nota barred cell; and (2) the cell fulfills the cell selection criteria.

Camping on a cell represents the state where a UE has completed the cellselection/reselection process and the UE has selected a cell formonitoring the system information and paging information.

3GPP is studying base stations referred to as Home-NodeB (Home-NB, HNB)and Home-eNodeB (Home-eNB, HeNB). HNB/HeNB is a base station for, forexample, household, corporation or commercial access service inUTRAN/E-UTRAN. Non-Patent Document 4 discloses three different modes ofthe access to the HeNB and HNB. Those are an open access mode, a closedaccess mode and a hybrid access mode. The respective modes have thefollowing characteristics. In the open access mode, the HeNB and HNB areoperated as a normal cell of a normal operator. In the closed accessmode, the HeNB and HNB are operated as a CSG cell. The CSG cell is acell where only CSG members are allowed access. In the hybrid accessmode, non-CSG members are allowed access at the same time. In otherwords, a cell in the hybrid access mode is the cell that supports boththe open access mode and the closed access mode. The cell in the hybridaccess mode is also referred to as a hybrid cell.

PRIOR ART DOCUMENTS Non-Patent Documents

Non-Patent Document 1: 3GPP TS36.300 V9.0.0 Chapter 4.6.1, Chapter4.6.2, Chapter 5 and Chapter 6

Non-Patent Document 2: 3GPP R1-072963

Non-Patent Document 3: TS36.304 V8.6.0 Chapter 3.1, Chapter 4.3 andChapter 5.2.4.8.1

Non-Patent Document 4: 3GPP S1-083461

Non-Patent Document 5: 3GPP R2-082899

Non-Patent Document 6: 3GPP TS22.220 V9.1.1

Non-Patent Document 7: 3GPP R2-093950

Non-Patent Document 8: 3GPP R3-091053

Non-Patent Document 9: 3GPP TS36.331

Non-Patent Document 10: 3GPP TS36.101

SUMMARY OF INVENTION Problem to be Solved by the Invention

Studied as the HeNB (HNB) service is an operation in which CSG membersbelonging to the same CSG are favored in terms of service and accountsetting in the CSG cell.

In order to allow the CSG members to receive those benefits, a UE who isa member of a CSG needs to favor the access to the cell of the same CSGto which the UE belongs over the access to the other cells. It isconceivable that the preferential access of the UE who is a CSG membermay also be applicable to a hybrid cell. The hybrid cell is a CSG cellwhere CSG members as well as non-CSG members are allowed access at thesame time. Therefore, at the hybrid cell, the access of CSG members whomake access in a closed access mode needs to be favored over the accessof non-CSG members who make access in an open access mode.

3GPP proposes that, as the method of preferentially allowing CSG membersaccess in a hybrid cell, UEs being CSG members are favored in cellreselection to a hybrid cell or from a hybrid cell, to thereby cause theUEs being CSG members to stay longer at a hybrid cell than the UEs beingnon-CSG members (Non-Patent Document 7).

As another method, it is also proposed to redirect UEs being non-CSGmembers to another cell in a case where a hybrid cell is congested(Non-Patent Document 8).

As proposed in Non-Patent Document 7 by 3GPP as the method ofpreferentially allowing the CSG members access at a hybrid cell, if theUEs being CSG members are favored in cell reselection to a hybrid cellor from a hybrid cell so as to stay longer at a hybrid cell than the UEsbeing non-CSG members, at times, the coverage in the closed access modebecomes larger than the coverage in the open access mode. In such acase, there occurs an area in which the UEs being CSG members and theUEs being non-CSG members have different access destinations, whichcauses a high degree of interference due to the access of both UEs. Theinterference increases a possibility that UEs being CSG members as wellas UEs being non-CSG members present in this area may result in accessfailure, and at worst, communication is not allowed in some cases. Thisproblem is not described in any prior document, and 3GPP has notdiscussed the problem at all.

An object of the present invention is to provide a mobile communicationsystem capable of eliminating a communication area in which a basestation serving as an access destination differs between UEs in a closedmode and UEs in an open mode.

Means to Solve the Problem

The present invention relates to a mobile communication system hybridlyallowing, in a case where an access group consisting of one or more userequipments and one or more base stations is registered, the base stationincluded in the access group to have access in a closed mode from theuser equipment included in the same access group and access in an openmode from a user equipment that is not included in the same accessgroup,

wherein a communication area of the base station in the open mode isidentical to a communication area of the base station in the closedmode.

Effects of the Invention

According to the present invention, a communication area of a basestation in an open mode and a communication area of a base station in aclosed mode are made identical to each other, which eliminates acommunication area in which a base station serving as an accessdestination differs between user equipments in the closed mode and userequipments in the open mode, leading to a significant reduction ofinterference.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating the configuration of an LTEcommunication system.

FIG. 2 is a diagram illustrating the configuration of a radio frame usedin the LTE communication system.

FIG. 3 is a diagram illustrating the configuration of a multimediabroadcast multicast service single frequency network (MBSFN) frame.

FIG. 4 is a diagram illustrating physical channels used in the LTEcommunication system.

FIG. 5 is a diagram illustrating transport channels used in the LTEcommunication system.

FIG. 6 is a diagram illustrating logical channels used in the LTEcommunication system.

FIG. 7 is a block diagram showing the overall configuration of a mobilecommunication system currently under discussion of 3GPP.

FIG. 8 is a block diagram showing the configuration of a user equipment71 according to the present invention.

FIG. 9 is a block diagram showing the configuration of a base station 72according to the present invention.

FIG. 10 is a block diagram showing the configuration of an MME accordingto the present invention.

FIG. 11 is a block diagram showing the configuration of a HeNBGWaccording to the present invention.

FIG. 12 is a flowchart showing an outline of cell search performed by auser equipment (UE) in the LTE communication system.

FIG. 13 is a conceptual diagram in a case where UEs being CSG membersare caused to stay longer at a hybrid cell than UEs being non-CSGmembers.

FIG. 14 is a conceptual diagram of interference occurring in an area inwhich only UEs being CSG members are allowed access.

FIG. 15 shows an operation example of a normal HO procedure currentlyunder discussion of 3GPP.

FIG. 16 shows an operation example in a case where redirection istriggered by a new RRC connection request from a UE being CSG member.

FIG. 17 shows an operation example in a case where redirection istriggered by checking of RRC connection.

FIG. 18 is a chart illustrating an operation of a UE in a case of an HOfailure, which is currently under discussion of 3GPP.

FIG. 19 shows a specific example of the operation of a UE in a case ofan HO failure according to the present invention.

FIG. 20 shows a sequence example in a case where a plurality of cellsare treated as target cells when a hybrid cell is congested.

FIG. 21 shows a sequence example in a case where HO requests areserially made to a plurality of target cells.

FIG. 22 shows a sequence example in a case where a desired number oftarget cells is set.

FIG. 23 shows a sequence example in a case where a plurality of targetcells are notified of the data required for continuing communication upto SN status information of PDCP related thereto.

FIG. 24 is a conceptual diagram in a case where the coverage for UEsbeing non-CSG members is made identical to the coverage for UEs beingCSG members.

FIG. 25 is a conceptual diagram in a case where the cell reselectionprocedures to/from a hybrid cell are made identical to each otherbetween UEs being non-CSG members and UEs being CSG members.

EMBODIMENTS FOR CARRYING OUT THE INVENTION First Embodiment

FIG. 7 is a block diagram showing an overall configuration of an LTEmobile communication system, which is currently under discussion of3GPP. Currently, 3GPP is studying an overall system configurationincluding closed subscriber group (CSG) cells (Home-eNodeBs (Home-eNBand HeNB) of e-UTRAN, Home-NB (HNB) of UTRAN) and non-CSG cells (eNodeB(eNB) of e-UTRAN, NodeB (NB) of UTRAN, and BSS of GERAN) and, as toe-UTRAN, is proposing the configuration of FIG. 7 (Chapter 4.6.1 ofNon-Patent Document 1).

FIG. 7 is described. A user equipment (UE) 71 performstransmission/reception to/from a base station 72. The base stations 72are classified into an eNB (non-CSG cell) 72-1 and Home-eNBs (CSG cells)72-2. The eNB 72-1 is connected to MMEs 73 through S1 interfaces, andcontrol information is communicated between the eNB and the MMEs. Aplurality of MMEs 73 are connected to one eNB 72-1. The eNBs areconnected to each other by means of an X2 interface, and controlinformation is communicated between the eNBs.

The Home-eNB 72-2 is connected to the MME 73 by means of the S1interface, and control information is communicated between the Home-eNBand the MME. A plurality of Home-eNBs are connected to one MME. While,the Home-eNBs 72-2 are connected to the MMEs 73 through a Home-eNBGateway (HeNBGW) 74. The Home-eNBs are connected to the HeNBGW by meansof the S1 interfaces, and the HeNBGW 74 is connected to the MMEs 73through an S1 interface. One or a plurality of Home-eNBs 72-2 areconnected to one HeNBGW 74, and information is communicated therebetweenthrough the S1 interface. The HeNBGW 74 is connected to one or aplurality of MMEs 73, and information is communicated therebetweenthrough the S1 interface.

Further, 3GPP is currently studying the configuration below. The X2interface between the Home-eNBs 72-2 is not supported. The HeNBGW 74appears to the MME 73 as the eNB 72-1. The HeNBGW 74 appears to theHome-eNB 72-2 as the MME 73. The S1 interface between the Home-eNB 72-2and the EPC is the same irrespective of whether or not the Home-eNB 72-2is connected to the EPC through the HeNBGW 74. The mobility to theHome-eNB 72-2 or the mobility from the Home-eNB 72-2 that spans the MMEs73 is not supported. The Home-eNB 72-2 supports a single cell.

FIG. 8 is a block diagram showing the configuration of the UE (equipment71 of FIG. 7) according to the present invention. The transmissionprocess of the UE shown in FIG. 8 is described. First, a transmissiondata buffer unit 803 stores the control data from a protocol processingunit 801 and the user data from an application unit 802. The data storedin the transmission data buffer unit 803 is transmitted to an encodingunit 804 and is subjected to encoding process such as error correction.There may exist the data output from the transmission data buffer unit803 directly to a modulating unit 805 without encoding process. The dataencoded by the encoding unit 804 is modulated by the modulating unit805. The modulated data is output to a frequency converting unit 806after being converted into a baseband signal, and then is converted intoa radio transmission frequency. After that, a transmission signal istransmitted from an antenna 807 to a base station 72. A UE 71 executesthe reception process as follows. The antenna 807 receives the radiosignal from the base station 72. The received signal is converted from aradio reception frequency to a baseband signal by the frequencyconverting unit 806 and is then demodulated by a demodulating unit 808.The demodulated data is transmitted to a decoding unit 809 and issubjected to decoding process such as error correction. Among the piecesof decoded data, the control data is transmitted to the protocolprocessing unit 801, while the user data is transmitted to theapplication unit 802. A series of process of the UE is controlled by acontrol unit 810. This means that, though not shown, the control unit810 is connected to the respective units (801 to 809).

FIG. 9 is a block diagram showing the configuration of the base station(base station 72 of FIG. 7) according to the present invention. Thetransmission process of the base station shown in FIG. 9 is described.An EPC communication unit 901 performs data transmission/receptionbetween the base station 72 and the EPCs (such as MME 73 and HeNBGW 74).A communication with another base station unit 902 performs datatransmission/reception to/from another base station. The X2 interfacebetween the Home-eNBs 72-2 is not intended to be supported, andaccordingly, it is conceivable that the communication with another basestation unit 902 may not exist in the Home-eNB 72-2. The EPCcommunication unit 901 and the communication with another base stationunit 902 respectively transmit/receive information to/from the protocolprocessing unit 903. The control data from the protocol processing unit903, and the user data and control data from the EPC communication unit901 and the communication with another base station unit 902 are storedin the transmission data buffer unit 904. The data stored in thetransmission data buffer unit 904 is transmitted to an encoding unit 905and is then subjected to encoding process such as error correction.There may exist the data output from the transmission data buffer unit904 directly to a modulating unit 906 without encoding process. Theencoded data is modulated by the modulating unit 906. The modulated datais output to a frequency converting unit 907 after being converted intoa baseband signal, and is then converted into a radio transmissionfrequency. After that, a transmission signal is transmitted from anantenna 908 to one or a plurality of UEs 71. While, the receptionprocess of the base station 72 is executed as follows. A radio signalfrom one or a plurality of UEs 71 is received by the antenna 908. Thereceived signal is converted from a radio reception frequency into abaseband signal by the frequency converting unit 907, and is thendemodulated by a demodulating unit 909. The demodulated data istransmitted to a decoding unit 910 and is then subjected to decodingprocess such as error correction. Among the pieces of decoded data, thecontrol data is transmitted to the protocol processing unit 903, EPCcommunication unit 901, or communication with another base station unit902, while the user data is transmitted to the EPC communication unit901 and communication with another base station unit 902. A series ofprocess by the base station 72 is controlled by a control unit 911. Thismeans that, though not shown, the control unit 911 is connected to therespective units (901 to 910).

The functions of the Home-eNB 72-2 currently under discussion of 3GPPare described below (Chapter 4.6.2 of Non-Patent Document 1). TheHome-eNB 72-2 has the same function as that of the eNB 72-1 and,further, has the following function in a case of connection to theHeNBGW 74. The Home-eNB 72-2 has a function of discovering a suitableserving HeNBGW 74. In a case where the Home-eNB 72-2 is connected to oneHeNBGW 74 only, that is, in a case of connection to the HeNBGW 74, theHome-eNB 72-2 does not use the Flex function of the S1 interface. Whenthe Home-eNB 72-2 is connected to the HeNBGW 74, it is notsimultaneously connected to another HeNBGW 74 or another MME 73. The TACand PLMN ID used by the Home-eNB 72-2 are supported by the HeNBGW 74.When the Home-eNB 72-2 is connected to the HeNBGW 74, selection of theMME 73 at “UE attachment” is performed by the HeNBGW 74 instead of theHome-eNB 72-2. The Home-eNB 72-2 may be deployed without networkplanning. Accordingly, the Home-eNB 72-2 may be moved from onegeographical area to another geographical area, and accordingly, may berequired to be connected to a different HeNBGW 74 depending on itslocation.

FIG. 10 is a block diagram showing the configuration of a mobilitymanagement entity (MME) according to the present invention. A PDN GWcommunication unit 1001 performs data transmission/reception between anMME 73 and a PDN GW. A base station communication unit 1002 performsdata transmission/reception between the MME 73 and the base station 72by means of the S1 interface. In the case where the data received fromthe PDN GW is user data, the user data is transmitted from the PDN GWcommunication unit 1001 to the base station communication unit 1002through a user plane processing unit 1003 and is then transmitted to oneor a plurality of base stations 72. In the case where the data receivedfrom the base station 72 is user data, the user data is transmitted fromthe base station communication unit 1002 to the PDN GW communicationunit 1001 through the user plane processing unit 1003 and is thentransmitted to the PDN GW.

In the case where the data received from the PDN GW is control data, thecontrol data is transmitted from the PDN GW communication unit 1001 to acontrol plane control unit 1005. In the case where the data receivedfrom the base station 72 is control data, the control data istransmitted from the base station communication unit 1002 to the controlplane control unit 1005. A HeNBGW communication unit 1004 is provided inthe case where the HeNBGW 74 is provided, which performs datatransmission/reception by means of the interface (IF) between the MME 73and the HeNBGW 74 according to an information type. The control datareceived from the HeNBGW communication unit 1004 is transmitted from theHeNBGW communication unit 1004 to the control plane control unit 1005.The processing results of the control plane control unit 1005 aretransmitted to the PDN GW through the PDN GW communication unit 1001.The processing results of the control plane control unit 1005 aretransmitted to one or a plurality of base stations 72 by means of the S1interface through the base station communication unit 1002, and aretransmitted to one or a plurality of HeNBGWs 74 through the HeNBGWcommunication unit 1004.

The control plane control unit 1005 includes a NAS security unit 1005-1,an SAE bearer control unit 1005-2 and an idle state mobility managingunit 1005-3, and performs overall process for the control plane. The NASsecurity unit 1005-1 provides, for example, security of a non-accessstratum (NAS) message. The SAE bearer control unit 1005-2 manages, forexample, a system architecture evolution (SAE) bearer. The idle statemobility managing unit 1005-3 performs, for example, mobility managementof an idle state (LTE-IDLE state, which is merely referred to as idle aswell), generation and control of paging signaling in an idle state,addition, deletion, update and search of a tracking area (TA) of one ora plurality of UEs 71 being served thereby, and TA list management. TheMME begins a paging protocol by transmitting a paging message to thecell belonging to a tracking area (TA) in which the UE is registered.The idle state mobility managing unit 1005-3 may manage the CSG of theHome-eNBs 72-2 to be connected to the MME, CSG-IDs and a whitelist. Inthe CSG-ID management, the relationship between a UE corresponding tothe CSG-ID and the CSG cell is managed (added, deleted, updated orsearched). For example, it may be the relationship between one or aplurality of UEs whose user access registration has been performed witha CSG-ID and the CSG cells belonging to this CSG-ID. In the whitelistmanagement, the relationship between the UE and the CSG-ID is managed(added, deleted, updated or searched). For example, one or a pluralityof CSG-IDs with which user registration has been performed by a UE maybe stored in the whitelist. The above-mentioned management related tothe CSG may be performed by another part of the MME 73. A series ofprocess by an MME 73 is controlled by a control unit 1006. This meansthat, though not shown, the control unit 1006 is connected to therespective units (1001 to 1005).

The function of the MME 73 currently under discussion of 3GPP isdescribed below (Chapter 4.6.2 of Non-Patent Document 1). The MME 73performs access control for one or a plurality of UEs being members ofclosed subscriber groups (CSGs). It is allowed for the MME 73 to performpaging optimization as an option.

FIG. 11 is a block diagram showing the configuration of the HeNBGWaccording to the present invention. An EPC communication unit 1101performs data transmission/reception between the HeNBGW 74 and the MME73 by means of the S1 interface. A base station communication unit 1102performs data transmission/reception between the HeNBGW 74 and theHome-eNB 72-2 by means of the S1 interface. A location processing unit1103 performs the process of transmitting, to a plurality of Home-eNBs,the registration information or the like among the data transmitted fromthe MME 73 through the EPC communication unit 1101. The data processedby the location processing unit 1103 is transmitted to the base stationcommunication unit 1102 and is transmitted to one or a plurality ofHome-eNBs 72-2 through the S1 interface. The data only caused to passthrough (to be transparent) without requiring the process by thelocation processing unit 1103 is passed from the EPC communication unit1101 to the base station communication unit 1102, and is transmitted toone or a plurality of Home-eNBs 72-2 through the S1 interface. A seriesof process by the HeNBGW 74 is controlled by a control unit 1104. Thismeans that, though not shown, the control unit 1104 is connected to therespective units (1101 to 1103).

The function of the HeNBGW 74 currently under discussion of 3GPP isdescribed below (Chapter 4.6.2 of Non-Patent Document 1). The HeNBGW 74relays an S1 application. The HeNBGW 74 terminates S1 applicationprocedures toward the Home-eNB 72-2 and towards the MME 73 that are notassociated with the UE 71. When the HeNBGW 74 is deployed, the procedurethat is not associated with the UE 71 is communicated between theHome-eNB 72-2 and the HeNBGW 74 and between the HeNBGW 74 and the MME73. The X2 interface is not set between the HeNBGW 74 and another node.The HeNBGW 74 recognizes the execution of paging optimization as anoption.

Next, an example of a typical cell search method in a mobilecommunication system is described. FIG. 12 is a flowchart showing anoutline from cell search to idle state operation performed by a userequipment (UE) in the LTE communication system. When the cell search isstarted by the UE, in Step ST1201, the slot timing and frame timing aresynchronized by a primary synchronization signal (P-SS) and a secondarysynchronization signal (S-SS) transmitted from a nearby base station.Synchronization codes, which correspond to physical cell identities(PCIs) assigned per cell one by one, are assigned to the synchronizationsignals (SS) including the P-SS and S-SS. The number of PCIs iscurrently studied in 504 ways, and these 504 ways are used forsynchronization, and the PCIs of the synchronized cells are detected(identified). Next, in Step ST1202, a reference signal RS of thesynchronized cells, which is transmitted from the base station per cell,is detected and the received power is measured. The code correspondingto the PCI one by one is used for the reference signal RS, andseparation from another cell is enabled by correlation using the code.The code for RS of the cell is derived from the PCI identified in StepST1201, which makes it possible to detect the RS and measure the RSreceived power. Next, in Step ST1203, the cell having the best RSreception quality (for example, cell having the highest RS receivedpower; best cell) is selected from one or more cells that have beendetected up to Step ST1202. In Step ST1204, next, the PBCH of the bestcell is received, and the BCCH that is the broadcast information isobtained. A master information block (MIB) containing the cellconfiguration information is mapped on the BCCH over the PBCH. Examplesof the MIB information include the down link (DL) system bandwidth (alsoreferred to as transmission bandwidth configuration (dl-bandwidth)),transmission antenna number and system frame number (SFN).

In Step ST1205, next, the DL-SCH of the cell is received based on thecell configuration information of the MIB, to thereby obtain a systeminformation block (SIB) 1 of the broadcast information BCCH. The SIB1contains the information related to access to the cell, informationrelated to cell selection and scheduling information of other SIB (SIBk;k is an integer equal to or larger than 2). In addition, the SIB1contains a tracking area code (TAC). In Step ST1206, next, the UEcompares the TAC received in Step ST1205 with the TAC that has beenalready possessed by the UE. In a case where they are identical to eachother as a result of comparison, the UE enters an idle state operationin the cell. In a case where they are different from each other as aresult of comparison, the UE requires a core network (EPC) (includingMME and the like) to change a TA through the cell for performingtracking area update (TAU). The core network updates the TA based on anidentification number (such as a UE-ID) of the UE transmitted from theUE together with a TAU request signal. The core network updates the TA,and then transmits the TAU received signal to the UE. The UE rewrites(updates) the TAC (or TAC list) of the UE with the TAC of the cell.After that, the UE enters the idle state operation in the cell.

In the LTE and universal mobile telecommunication system (UMTS), theintroduction of a closed subscriber group (CSG) cell is studied. Asdescribed above, access is allowed for only one or a plurality of UEsregistered with the CSG cell. One or a plurality of UEs registered withthe CSG cell constitute one CSG. A specific identification numberreferred to as CSG-ID is added to the thus constituted CSG. Note thatone CSG may contain a plurality of CSG cells. After being registeredwith any one of the CSG cells, the UE can access the other CSG cells ofthe CSG to which the registered CSG cell belongs. Alternatively, theHome-eNB in the LTE or the Home-NB in the UMTS is used as the CSG cellin some cases. The UE registered with the CSG cell has a whitelist.Specifically, the whiltelist is stored in the SIM/USIM. The CSGinformation of the CSG cell with which the UE has been registered islisted in the whitelist. Specific examples of the CSG informationinclude CSG-ID, tracking area identity (TAI) and TAC. Any one of theCSG-ID and TAC is adequate as long as they are associated with eachother. Alternatively, GCI is adequate as long as the CSG-ID, TAC andglobal cell identity (GCI) are associated with each other. As can beseen from the above, the UE which does not have a whitelist (including acase where the whitelist is empty in the present invention) is notallowed to access the CSG cell but is allowed to access only the non-CSGcell. On the other hand, the UE which has a whitelist is allowed toaccess the CSG cell of the CSG-ID with which registration has beenperformed as well as the non-CSG cell.

3GPP discusses that all physical cell identities (PCIs) are split(referred to as PCI-split) into ones reserved for CSG cells and theothers reserved for non-CSG cells (Non-Patent Document 5). Further, 3GPPdiscusses that the PCI split information is broadcast in the systeminformation from the base station to the UEs being served thereby.Disclosed here is the basic operation of a UE by PCI split. The UE thatdoes not have the PCI split information needs to perform cell searchusing all PCIs (for example, using all 504 codes). On the other hand,the UE that has the PCI split information is capable of performing cellsearch using the PCI split information.

3GPP allows temporary CSG members. A temporary member is also referredto as a temporary member or visitor. It is possible to configure a timeperiod for a temporary member to be considered as a CSG member(Non-Patent Document 6).

In 3GPP, there are two modes in the method of selecting or reselecting aCSG cell by a UE. One is an automatic mode. The feature of the automaticmode is described below. The UE performs selection or reselection withthe use of an allowed CSG ID list in the UE. After the completion ofPLMN selection, the UE camps on one cell in the selected PLMN only in acase of a non-CSG cell or a CSG cell with a CSG ID present in theallowed CSG list. The UE disables an autonomous search function of theCSG cell if the allowed CSG list of the UE is empty (Chapter 5.2.4.8.1of Non-Patent Document 3).

The second is a manual mode. The feature of the manual mode is describedbelow. The UE shows a list of available CSGs in the currently selectedPLMN. The list of CSGs provided to the user by the UE is not limited tothe CSGs included in the allowed CSG list stored in the UE. The userselects the CSG based on the list of CSGs, and then the UE camps on thecell with the selected CSG ID, to thereby attempt registration (Chapter5.2.4.8.1 of Non-Patent Document 3).

Non-Patent Document 7 proposed by 3GPP discloses, as the method ofpreferentially allowing access to CSG members at a hybrid cell, thetechnique in which UEs being CSG members are favored in cell reselectionto a hybrid cell or from a hybrid cell to another cell or cellreselection from another cell to a hybrid cell, to thereby cause the UEsbeing CSG members to stay longer at a hybrid cell than UEs being non-CSGmembers. As a result of UEs being CSG members being caused to staylonger at a hybrid cell than UEs being non-CSG members, the coverage ina closed access mode becomes larger than the coverage in an open accessmode in some cases.

FIG. 13 is a conceptual diagram in a case where UEs being CSG membersare caused to stay longer at a hybrid cell than UEs being non-CSGmembers. In the diagram, 1301 denotes a non-CSG cell, which is a macrocell (eNB) as an example in this case. 1302 denotes the coverage of thenon-CSG cell. 1303 denotes a hybrid cell (HeNB in a hybrid access mode).1304 denotes the coverage accessible at the hybrid cell in an openaccess mode as well as a closed access mode. 1305 (shaded portion)denotes the coverage accessible at the hybrid cell only in the closedaccess mode. 1306 denotes a UE being the member of the same CSG as theCSG to which the hybrid cell belongs. 1307 denotes a UE being a non-CSGmember. The UE being a CSG member communicates with the non-CSG cell1301 out of the area of the coverage 1305, and the UE 1306 that hasmoved to the area of the coverage 1305 communicates with the hybrid cell1303 through cell reselection. The UE 1307 being a non-CSG member stillcommunicates with the non-CSG cell 1301 also in the area of the coverage1305, and communicates with the hybrid cell 1303 through cellreselection only after moving to the coverage 1304.

In this manner, if the UEs being CSG members are caused to stay longerat a hybrid cell than the UEs being non-CSG members, correspondingly,the coverage in the closed access mode becomes larger than the coveragein the open access mode in some cases. This is because there occurs anarea in which only the UEs being CSG members are allowed to access thehybrid cell. In such an area (shaded portion in the diagram), the UEsbeing CSG members access the hybrid cell, whereas the UEs being non-CSGmembers access the other cell (in the diagram, macro cell). Aninterference problem as described below occurs in the situation in whichsuch an area occurs.

FIG. 14 is a conceptual diagram of the interference occurring in thearea in which only UEs being CSG members are allowed access. Part (a) ofFIG. 14 shows the interference occurring in uplink communication, andPart (b) of FIG. 14 shows the interference occurring in downlinkcommunication. Description of the parts denoted by the same numbers asthose of FIG. 13 in FIG. 14 is omitted. In the diagram, a solid arrowindicates a signal and a dotted arrow indicates interference.

Part (a) of FIG. 14 is described. In the area (shaded portion in thediagram) 1305 in which only UEs being CSG members are allowed to accessa hybrid cell, the UE (1306) being a CSG member accesses the hybrid cell(1303), and the UE (1307) being a non-CSG member accesses the macro cell(1301). This causes the interference described below in uplinkcommunication. An uplink signal wave from the UE (1307) being a non-CSGmember to the macro cell (1301) causes interference to an uplink signalwave of the UE (1306) being a CSG member being served by a hybrid cell(1401). An uplink signal wave from the UE (1306) being a CSG member tothe hybrid cell (1303) causes interference to an uplink signal wave ofthe UE (1307) being a non-CSG member being served by a macro cell(1402). Part (b) of FIG. 14 is described. In the area (shaded portion inthe diagram) 1305 in which only UEs being CSG members are allowed toaccess a hybrid cell, the UE (1306) being a CSG member accesses thehybrid cell (1303), and the UE (1307) being a non-CSG member accessesthe macro cell (1301). This causes the interference described below indownlink communication. A downlink signal wave from the hybrid cell(1303) to the UE (1306) being a CSG member causes interference to adownlink signal wave of the UE (1307) being a non-CSG member beingserved by a macro cell (1403). A downlink signal wave from the macrocell (1301) to the UE (1307) being a non-CSG member causes interferenceto a downlink signal wave to the UE (1306) being a CSG member beingserved by the hybrid cell (1404).

In this manner, in the area in which only UEs being CSG members areallowed access, a high degree of interference occurs by the access ofboth UEs when the access destination differs between UEs being CSGmembers and UEs being non-CSG members. The interference increases apossibility that UEs being CSG members as well as UEs being non-CSGmembers present in this area may fail in access, and further,communication may not be allowed in some cases. In other words, thereoccurs an area in which communication becomes impossible for UEs beingCSG members and/or UEs being non-CSG members. This problem is notdescribed in any prior document, and 3GPP has not discussed the problemat all.

The present embodiment discloses the method of solving theabove-mentioned problem. At the hybrid cell, the coverage for UEs beingnon-CSG members is made identical to the coverage for UEs being CSGmembers. In other words, the communication area of a cell (base station)in an open access mode is made identical to the communication area of acell (base station) in a closed access mode. As a specific method,parameters that define the coverage used at the hybrid cell are madeidentical to each other between UEs being non-CSG members and UEs beingCSG members. Alternatively, the same parameter values are applied toboth UEs (UEs being CSG members and UEs being non-CSG members). Examplesof the parameters regarding the coverage used at a hybrid cell includethe maximum transmission power from a cell, a tilt angle of an antennaof a cell and the maximum allowed transmission power of each UE beingserved by a cell. The maximum allowed transmission power of a UE is aparameter that enables to limit the uplink transmission power of a UE,as described in Non-Patent Document 10.

FIG. 24 is a conceptual diagram in a case where the coverage for UEsbeing non-CSG members is made identical to the coverage for UEs beingCSG members. In the diagram, 2401 denotes a non-CSG cell, which is amacro cell (eNB) here. 2402 denotes the coverage of the non-CSG cell.2403 denotes a hybrid cell (HeNB in a hybrid access mode). 2404 denotesthe coverage accessible at the hybrid cell in an open access mode aswell as a closed access mode. 2405 denotes a UE being the member of thesame CSG as the CSG to which the hybrid cell belongs. 2406 denotes a UEbeing a non-CSG member.

The macro cell (2401) is not a cell in a hybrid access mode similarly toa hybrid cell but is a cell only in an open access mode. For thisreason, one coverage is provided for the macro cell (2401) no matterwhich a UE is being served by the macro cell (2401) (2402). In thiscase, similarly also at the hybrid cell (2403), one coverage is providedfor the hybrid cell (2403) no matter which a UE is being served thereby(2404).

Through the above, the UE (2405) being a CSG member and the UE (2406)being a non-CSG member communicate with the non-CSG cell (2401) outsidethe coverage (2404) of the hybrid cell (2403). On the other hand, withinthe coverage (2404) of the hybrid cell, the UE (2405) being a CSG memberand the UE (2406) being a non-CSG member communicate with the hybridcell (2403). Accordingly, it is possible to eliminate the area in whichthe access destination differs between the UEs being CSG members and UEsbeing non-CSG members as shown in part (a) of FIG. 14 and part (b) ofFIG. 14, which eliminates uplink and/or downlink interference occurringin the area.

The method disclosed in the present embodiment enables to eliminate thearea in which UEs being CSG members and/or UEs being non-CSG memberscannot perform communication in a case where a hybrid cell is deployedin a system. Accordingly, a hybrid cell can be deployed flexibly in thesystem, which allows the provision of various services.

The control processing at a hybrid cell can be simplified by making theparameters that define the coverage used at the hybrid cell identical toeach other between UEs being non-CSG members and UEs being CSG membersor by applying the same parameter values to both UEs. In addition, owingto application of the same parameter values to both UEs, control is notrequired to differ depending on a parameter, leading to simplificationof control processing in a UE as well. Further, the number of parametersat a hybrid cell can be reduced, and the number of parameters that needto be notified to UEs being served thereby can be reduced as well,leading to a reduction of a signaling amount. This achieves effects suchas effective use of radio resources.

Second Embodiment

The present embodiment discloses another method for solving theabove-mentioned problem. In cell reselection from a hybrid cell toanother cell and cell reselection from another cell to a hybrid cell,the criteria such as the procedures, rules and a cell ranking criteriaof the reselection are made identical to each other between UEs beingnon-CSG members and UEs being CSG members. As a specific method, theparameters that define the criteria used in cell reselection from ahybrid cell to another cell and cell reselection from another cell to ahybrid cell are made identical to each other between both UEs, or thesame parameter values are used therebetween. Examples of the parametersthat define the criteria used in cell reselection from a hybrid cell toanother cell and cell reselection from another cell to a hybrid cellinclude reception quality thresholds (Sintrasearch, Sintersearch) of aserving cell for initiating cell reselection and an offset value(Qoffset) applied to the measurement results of the reception quality ofthe cell in the criteria of cell ranking.

FIG. 25 is a conceptual diagram in a case where the cell reselectioncriteria to/from a hybrid cell are made identical to each other betweenUEs being non-CSG members and UEs being CSG members. In the diagram, thedescription of the same numbers as those of FIG. 24 is omitted. If theUE (2406) being a non-CSG member being served by the macro cell (2401)and the UE (2405) being a CSG member are located at the same position,by making the criteria of cell reselection to the hybrid cell (2403)identical to each other between the UE (2406) being a non-CSG member andthe UE (2405) being a CSG member, the both UEs perform cell reselectionto the hybrid cell (2403) at the same position when the otherenvironment of radio waves is the same. If the UE (2406) being a non-CSGmember being served by the hybrid cell (2403) and the UE (2405) being aCSG member are located at the same position, by making the criteria ofcell reselection from the hybrid cell (2403) identical to each otherbetween the UE (2406) being a non-CSG member and the UE (2405) being aCSG member, the both UEs perform cell reselection to the macro cell(2401) at the same position when the other environment of radio waves isthe same.

Accordingly, whether the UE being served by the hybrid cell (2403) is aCSG member or a non-CSG member at the hybrid cell (2403), one coveragecan be provided (2404) as the hybrid cell (2403). This causes the UE(2405) being a CSG member and the UE (2406) being a non-CSG member tobecome capable of communicating with the non-CSG cell (2401) out of thecoverage (2404) of the hybrid cell (2403). On the other hand, in thecoverage (2404) of a hybrid cell, the UE (2405) being a CSG member andthe UE (2406) being a non-CSG member communicate with the hybrid cell(2403). Accordingly, it is possible to eliminate the area in which theaccess destination differs between UEs being CSG members and UEs beingnon-CSG members as shown in part (a) of FIG. 14 and part (b) of FIG. 14,which eliminates uplink and/or downlink interference occurring in thearea.

The method disclosed in the present embodiment enables to eliminate thearea in which UEs being CSG members and/or UEs being non-CSG memberscannot perform communication in a case where a hybrid cell is deployedin the system. Accordingly, a hybrid cell can be deployed flexibly inthe system, which enables to provide various services.

In cell reselection to/from a hybrid cell, the control processing at acell can be simplified by making the criteria such as the procedures,rules and a cell ranking criteria of the reselection identical to eachother between UEs being non-CSG members and UEs being CSG members. Inaddition, the same parameter values are applied to both UEs, and thusthe control is not required to differ depending on a parameter, leadingto simplification of control processing in a UE as well. Further, thenumber of parameters used at a cell can be reduced, and the number ofparameters that need to be notified to UEs being served thereby can bereduced as well, leading to a reduction of a signaling amount. Thisachieves an effect of such as effective use of radio resources.

Third Embodiment

The present embodiment discloses another method for solving theabove-mentioned problem. The second embodiment has disclosed the case ofcell reselection to/from a hybrid cell. That is, it is possible toeliminate the area in which the access destination differs between UEsbeing CSG members and UEs being non-CSG members for the UE in anRRC_Idle state, which eliminates uplink and/or downlink interferenceoccurring in the area.

The present embodiment discloses the method capable of eliminating anarea in which the access destination differs between UEs being CSGmembers and UEs being non-CSG members for a UE in an RRC_connectedstate, to thereby eliminate uplink and/or downlink interferenceoccurring in the area.

In handover (outbound HO) from a hybrid cell to another cell andhandover (inbound HO) from another cell to a hybrid cell, the criteriainclude the criteria used in the procedures, rules and a criteria of theHO are made identical to each other between the UEs being non-CSGmembers and the UEs being CSG members. As a specific method, theparameters that define the criteria of HO to/from a hybrid cell are madeidentical to each other between both UEs or the same parameter valuesare used. Examples of the parameters that define the criteria of HOto/from hybrid cells include parameters serving as judgment index fordetermining whether or not an event triggering a measurement reportoccurs. They include thresholds (Thresh, Thresh1, Thresh2) of eventoccurrence, an offset value (Ocs) of a serving cell that is applied tothe measurement results of the reception quality, an offset value (Ofs)of the frequency of a serving cell that is applied to the measurementresults of the reception quality, an offset value (Ocn) of neighborcells that is applied to the measurement results of the receptionquality, an offset value (Ofn) of the frequency of neighbor cells thatis applied to the measurement results of the reception quality, anoffset value (Off) for each event and a hysteresis (Hys) for each event.

This enables to make the coverage of hybrid cells identical to eachother between the UEs being CSG members in the RRC connected state andUEs being non-CSG members in the RRC connected state. Accordingly, it ispossible to eliminate the area in which the access destination differsbetween UEs being CSG members and UEs being non-CSG members as shown inpart (a) of FIG. 14 and part (b) of FIG. 14, which eliminates uplinkand/or downlink interference occurring in the area.

The method disclosed in the present embodiment can eliminate the area inwhich UEs being CSG members and/or UEs being non-CSG members cannotperform communication in a case where a hybrid cell is deployed in thesystem. This enables to flexibly deploy a hybrid cell in the system,whereby various services can be provided.

In HO to/from a hybrid cell, it is possible to simplify the controlprocessing in the cell by making the criteria such as the procedures,rules and criteria of HO identical to each other between UEs beingnon-CSG members and UEs being CSG members. In addition, the sameparameter values are applied to both UEs, and thus control is notrequired to differ depending on a parameter, which also leads tosimplification of the control processing in the UE. Further, the numberof parameters used in the cell can be reduced, and the number ofparameters that need to be notified to UEs being served thereby can bereduced, leading to a reduction of a signaling amount. This enables toachieve effects such as effective use of radio resources.

The first embodiment to the third embodiment may be used in combination.Accordingly, it is possible to eliminate the area in which UEs being CSGmembers and/or UEs being non-CSG members cannot perform communication inany of the RRC-Idle state and RRC connected state of a UE or in theoperation when the UE changes between the RRC-Idle state and RRCconnected state.

Fourth Embodiment

The description has been given of a suggestion by 3GPP that, as anothermethod of giving preferential access to CSG members at a hybrid cell,UEs being non-CSG members are redirected to another cell in a case wherethe hybrid cell is congested (Non-Patent Document 8). In addition,Non-Patent Document 8 describes that at a hybrid cell in a congestedstate, UEs being non-CSG members that have been in the RRC-Connectedstate are redirected to another cell.

However, there is no specific description regarding the way ofredirection, which causes a problem that practical operations cannot bemade.

The present embodiment discloses the method for solving this problem. Asa specific method of redirecting the UEs being non-CSG members that havebeen in the RRC_Connected state to another cell, in a case where a cellreceives a new RRC connection request from UEs being CSG members at ahybrid cell in a congested state, the procedure of redirecting the UEsbeing non-CSG members to another cell is triggered by this connectionrequest. As a specific method of redirection, the UEs being non-CSGmembers are caused to hand over (HO) to another cell.

First, FIG. 15 shows an operation example of a normal HO procedure(Non-Patent Document 1). This is an example of the HO procedurediscussed by 3GPP. Described here is the case in which communicationbetween a source cell and a target cell is performed by means of an X2interface.

In Step ST1501, a source cell notifies the UE of a measurement controlmessage and causes the UE to perform measurement. In Step ST1502, the UEnotifies the source cell of measurement results. In Step ST1503, thesource cell determines a target cell with the use of a measurementreport from the UE. In this manner, in normal HO, each cell judgeswhether or not the cell needs to cause the UE to perform HO or to whichcell the cell causes the UE to perform HO, mainly based on themeasurement results of the reception quality of the UE. That is, the HOprocedure is triggered by the measurement report from the UE (StepST1502).

In Step ST1504, the source cell that has determined a target cellnotifies the target cell of an HO request message. The HO requestmessage contains UE context information that is the informationregarding the UE that is caused to perform HO. In Step ST1505, thetarget cell determines whether to cause the UE to perform HO inconsideration of the state of the own cell and the information regardingthe UE. Described here is the case where HO is allowed. In the casewhere HO is allowed, the target cell notifies an allowance message (Ack)for the HO request in Step ST1506. In Step ST1507, the source cell thathas received the allowance message notifies the UE of HO controlinformation.

In Step ST1509, the source cell notifies the target cell of the datarequired for continuing communication in HO and the SN statusinformation of PDCP related thereto. The UE that has received the HOcontrol information in Step ST1507 is detached from the source cell inStep ST1508, and in Step ST1510, performs synchronization with thetarget cell based on the target cell information contained in the HOcontrol information. After the establishment of synchronization, in StepST1511, the target cell notifies the UE of allocation information ofuplink resources as well as timing advance (TA) information that istransmission timing information. In Step ST1512, the UE that hasreceived the information notifies the target cell of an RRC connectionreconfiguration complete message. As a result, data communication isstarted between the UE and the target cell.

In Step ST1513, the target cell that has received Step ST1512 performsthe processing for HO completion with the source cell through an MME orserving GW (S-GW) being an entity of higher layer. Along with theprocessing for HO completion of Step ST1513, in Step ST1514, the sourcecell releases the resources used in control associated with theinformation regarding the UE.

In the HO procedure, the transmission of an HO request by the sourcecell in Step ST1504 through the transmission of HO control informationby the source cell in Step ST1507 are treated as an HO preparation step,the detachment of the UE in Step ST1508 and the transmission of SNstatus information by the source cell in Step ST1509 through thereception of the RRC connection reconfiguration completion by the targetcell in Step ST1512 are treated as an HO execution step, and the startof processing for HO completion in Step ST1513 and the release ofresources by the source cell in Step ST1514 are treated as an HOcompletion step.

Next, a specific method in the present embodiment is disclosed. FIG. 16shows an operation example in the case where the hybrid cell in thecongested state redirects the UE being a non-CSG member to another cellin response to a new RRC connection request from the UE being a CSGmember. HO is used as a specific method of redirection. In the figure,description of the parts of the same step numbers as those of FIG. 15 isomitted. In this example, the source cell is a hybrid cell. Here, thetarget cell is a cell A without limiting the access mode of the targetcell.

The case where a non-CSG member is in the RRC connected state at ahybrid cell is described (Step ST1612). The UE being a non-CSG membermay perform services such as data communication with a core network side(such as MME or S-GW) through the hybrid cell. In Step ST1601, the UEbeing a CSG member being served by the hybrid cell transmits an RRCconnection request. In Step ST1602, the hybrid cell in a congested statethat has received the RRC connection request message determines a UEbeing a non-CSG member in the RRC connected state which the cellredirects at the own cell. Here, HO to another cell is redirection. Asdescribed above, normal HO is triggered mainly by the measurementresults of reception quality of the UE. In the present embodiment,however, HO is triggered by the reception of a new RRC connectionrequest from the UE being a CSG member at the hybrid cell in thecongested state. In addition, the connection between a UE in a closedmode and a hybrid cell (base station) is completed after the UE in anopen mode is redirected (HO) to another cell (base station) from thehybrid cell (base station). This enables to start the HO procedure atthe timing of a new RRC connection request of a UE being a CSG member(UE in a closed mode), leading to a reduction of a control delay untilthe UE being a CSG member is allowed communication.

The hybrid cell that has determined the UE being a non-CSG member whichthe cell causes to perform HO in Step ST1602 starts the processing ofcausing the UE being a non-CSG member to perform HO to another cell. Thehybrid cell notifies UE being the non-CSG member of a measurementcontrol message in Step ST1501, and in Step ST1502, the UE notifies thehybrid cell of the measurement results. Differently from the procedureshown in FIG. 15, in Step ST1605 and Step ST1606, the hybrid cell thathas determined the target cell in Step ST1503 transmits a message torequest an HO to the target cell through the MME. As shown in FIG. 7, inthe current architecture of the HeNB by 3GPP, there is no X2 interfacebetween cells and the HeNBs are connected to each other by means of theS1 interface through the MME, HeNBGW or S-GW. Accordingly, the messagebetween the hybrid cell being a source cell and the target cell may becommunicated through the MME/HeNBGW/S-GW. The HO request messagecontains the information regarding the UE to be caused to perform HO. InStep ST1505, the target cell determines whether or not to cause the UEto perform HO in consideration of the state of the own cell and theinformation regarding the UE. Described here is the case where HO isallowed. When HO is allowed, in Step ST1607 and Step ST1608, the targetcell notifies an allowance message for the HO request through the MME orthe like. This may also be performed through the MME or the like becausean X2 interface is not provided. In Step ST1507, the source cell thathas received the allowance message notifies the UE of the HO controlinformation. Further, for the target cell, in Step ST1609 and StepST1610, the source cell notifies the target cell of the data requiredfor continuing communication in HO and the SN status information of thePDCP related thereto. The data may be notified not through the MME orHeNBGW but through the S-GW. Then, as in FIG. 15, Step ST1508 throughStep ST1514 are performed.

Upon the completion of HO in Step ST1514, in Step ST1603, the hybridcell notifies the UE being a CSG member that has requested RRCconnection of an RRC connection setup message. The UE being a CSG memberthat has received the setup message performs setup, and in Step ST1604,notifies the hybrid cell of an RRC connection setup complete message.This enables the UE being a CSG member to be provided services such asdata communication with the core network side (such as MME) through thehybrid cell.

Meanwhile, the UE being a non-CSG member notifies the target cell of theRRC connection reconfiguration complete message in Step ST1512, wherebydata communication between the UE and the target cell is started. Thisallows the non-CSG member to perform communication at the target cellwhile keeping the RRC connected state.

In the specific example shown in FIG. 16, the UE notifies the hybridcell of the measurement results in Step ST1502, and in Step ST1503, thehybrid cell determines a target cell based on that information. StepST1501 and Step ST1502 may not be performed after the determination of aUE being a non-CSG member to be caused to perform HO in Step ST1602, notby this method. Step ST1503 is performed after Step ST1602. If thehybrid cell recognizes the cell present in the vicinity thereof, it maydetermine a target cell based on that. Examples of the method in whichthe hybrid cell recognizes the cell present in the vicinity thereofinclude the method of measuring the reception quality from a neighborcell by the HeNB and using the results thereof and the method using themeasurement results from another UE being served by the hybrid cell. Thetime period until performing redirection (HO) can be reduced by omittingStep ST1501 and Step ST1502, which makes it possible to reduce the timeperiod until the UE being a CSG member can receive the service as a CSGmember at a hybrid cell or the time period until a non-CSG member canperform communication at another cell.

While the procedure of completing RRC connection of a UE being a CSGmember is performed after the completion of redirection (HO) of a UEbeing a non-CSG member in the example above, redirection (HO) of a UEbeing a non-CSG member and the RRC connection procedure of a UE being aCSG member may be performed simultaneously. This enables to complete theRRC connection procedure of the UE being a CSG member to the hybrid celleven if the redirection (HO) of a UE being a non-CSG member fails,whereby a UE being a CSG member is given preferential access.

In this manner, the RRC connection request from a UE being a CSG memberis used as the trigger for the hybrid cell in a congested state toredirect a UE being a non-CSG member, whereby the UE being a CSG membercan establish RRC connection at the hybrid cell and transmit/receivedata to/from the network side, and accordingly can receive the servicesas the CSG member at the hybrid cell.

Further, also in the case where the hybrid cell in a congested statelacks resources for RRC connection, by redirecting the UE being anon-CSG member before the completion of RRC connection with an RRCconnection request from a UE being a CSG member as the trigger, it ispossible to redirect the UE being a non-CSG member and allow RRCconnection of the CSG member.

First Modification of Fourth Embodiment

As another specific method of redirecting a UE being a non-CSG memberthat has been in RRC_Connected state to another cell, at a hybrid cellin a congested state, a new RRC connection request is made from the UEbeing a CSG member and, in a case where the hybrid cell receives the RRCconnection completion, the procedure of redirecting the UE being anon-CSG member to another cell is triggered by the completion of RRCconnection.

As an example, FIG. 17 shows the method of activating the redirection ofa UE being a non-CSG member to another cell in response to the RRCconnection setup complete message, as RRC connection completion. HO isused as a specific method of redirection. In the figure, Step ST1611 isidentical to a series of processing of Step ST1611 shown in FIG. 16.

The case where the non-CSG member is in the RRC connected state at ahybrid cell is described (Step ST1705). The UE being a non-CSG membermay be provided services such as data communication with the corenetwork side (such as MME) through the hybrid cell. In Step ST1701, theUE being a CSG member being served by the hybrid cell transmits an RRCconnection request. In Step ST1702, the hybrid cell notifies the UEbeing a CSG member that has requested RRC connection of the RRCconnection setup message. The UE being a CSG member that has receivedthe setup message performs setup, and in Step ST1703, notifies thehybrid cell of the RRC connection setup complete message. In StepST1704, the hybrid cell in a congested state that has received the RRCconnection setup complete message determines a UE being a non-CSG memberin the RRC connected state which the cell redirects at the own cell.Here, HO to another cell is redirection. HO is triggered by reception ofa new RRC connection setup complete message from the UE being a CSGmember at a hybrid cell in a congested state. In other words, after thecompletion of connection between the UE in a closed mode and a hybridcell (base station), the UE in an open mode is redirected to anothercell (base station) from the hybrid cell (base station).

Accordingly, the UE being a CSG member enters the RRC connected state,and thus is prepared to perform data communication with the core networkat any time. Therefore, in a case where, for example, another UE being anon-CSG member in an RRC connected state that is being served by thehybrid cell ends communication or changes to the RRC_Idle state, evenwhen the UE being a non-CSG member to perform redirection (HO) has notcompleted HO, the CSG member can communicate with the core networkthrough a hybrid cell, and accordingly is capable of receiving theservice as a CSG member.

HO is used as the specific method of redirection in the specific exampledescribed above. It may be, not limited to HO, release of RRC connectionfrom a hybrid cell, or camping on another cell after the release of RRCconnection from a hybrid cell. As a method of camping on another cell,cell selection or cell reselection may be performed. On this occasion,selection to the hybrid cell whose RRC connection has been released isprohibited. A timer may be provided with the constant time period forprohibition. This prevents the situation in which cell selection or cellreselection cannot be performed to the hybrid cell permanently. Thismethod does not allow a UE being a non-CSG member to continue the RRCconnected state but allows the UE to establish RRC connection again atanother cell.

Fifth Embodiment

Non-Patent Document 8 describes the method of, in a case where thehybrid cell is congested, changing (from FALSE to TRUE) a CSG-indicatorbeing broadcast information of a cell when the UE being a non-CSG memberis redirected to another cell. The CSG-indicator is included in theSIB1, and TRUE is set in a case of a CSG cell only in a closed accessmode, whereas FALSE is set in a case of a non-CSG cell only in an openaccess mode or a hybrid cell in a hybrid mode. Therefore, as a result ofchanging (from FALSE to TRUE) the CSG-indicator of a hybrid cell, thehybrid cell is caused to operate as a CSG cell only in a closed accessmode, which prevents the UE being a non-CSG member from accessing thehybrid cell.

However, in a case where HO is used as a specific method of redirectinga UE being a non-CSG member that has been in the RRC-Connected state toanother cell, a problem arises when this method is performed. Normally,the HO procedure returns to the setting of a source cell in a case whereHO to the target cell fails (HO failure, HOF). This is also referred toas reverting back.

FIG. 18 shows the operation of the UE in an HO failure in 3GPP standards(Non-Patent Document 9). When the UE detects an HO failure in StepST1801, in Step ST1802, the UE returns to the setting of a source celland starts a re-establishment procedure of RRC connection. In there-establishment procedure of RRC connection, the UE starts T311 (StepST1803). T311 is a timer of the time period that is allowed for there-establishment procedure of RRC connection. The UE returns to thesetting of a source cell in Step ST1802, and thus selects a source cellas a suitable cell. In the case of selecting a suitable cell, the UEimmediately moves to Step ST1804 (A). In Step ST1804, the UE stops thetimer 311 and starts T301, to thereby transmit an RRC connectionre-establishment request to the source cell. T301 is a timer of the timeperiod allowed for the UE to receive an RRC connection re-establishmentmessage from the source cell. After that, in a case where the UE failsto receive the RRC connection re-establishment message and T301 expires(Step ST1805), the UE moves to Step ST1806 and judges that the RRCconnection re-establishment has failed, and then leaves from the RRCconnected state.

As shown in FIG. 18, also in the 3GPP standards, a UE returns to thesetting of a source cell when it fails in HO to a target cell. Normally,the source cell is a cell that has been accessed, and accordingly, is asuitable cell. That is, the UE reverts back to the source cell in a caseof a normal HO failure, and always performs the procedure in the case ofselecting a suitable cell (A).

However, a problem arises in a case where a CSG-indicator of the SIB1 ofa hybrid cell in a congested state is changed (from FALSE to TRUE), andaccordingly the hybrid cell is caused to operate as a CSG cell only in aclosed access mode and the UE being a non-CSG member that has been inthe RRC connected state is caused to perform HO to another cell. This isbecause the source cell (concerned hybrid cell) in the HO procedure isno longer a suitable cell for the UE being a non-CSG member. This isbecause the CSG-indicator is TRUE at the hybrid cell (concerned sourcecell) in a congested state. In a case where the CSG-indicator is TRUE,only the UE being the same CSG member can be treated as a suitable cell.Therefore, the UE being a non-CSG member is no longer a suitable cell.

In such a case, the hybrid cell (concerned source cell) is no longer asuitable cell even when the UE being a non-CSG member returns to thesetting of the source cell due to an HO failure, and thus the UE can donothing but to wait the expiration of the timer of T311 (B). In StepST1807, the UE moves to Step ST1806 upon expiration of the T311 timerand fails to re-establish RRC connection, which has to leave from theRRC connected state. As described above, the case of performing a normalHO procedure for redirecting a UE being a non-CSG member causes aproblem that RRC connection cannot always be re-established in an HOfailure. Further, the UE always has to wait the time period when T311expires before leaving the RRC connected state in an HO failure, andwastefully spends a time period until leaving the RRC connected statefor enabling the next operation.

Those problems are not described in any prior art document and is notdiscussed by 3GPP.

In order to solve the above-mentioned problems, in the presentembodiment, the CSG-indicator of the SIB1 of a hybrid cell in acongested state is changed (from FALSE to TRUE) after successfulredirection of a UE being a non-CSG member.

As described above, a setting change so as to disable reverting back tothe hybrid cell (base station) is executed after the successfulhandover, which enables the UE being a non-CSG member caused to performHO by the hybrid cell in a congested state to revert back to the sourcecell even in the case of an HO failure to a target cell. Therefore, withreference to FIG. 18, the UE being a non-CSG member is capable ofexecuting Step ST1804 by a route A. This allows the UE to re-establishRRC connection.

Further, the hybrid cell can also execute HO again to the UE being anon-CSG member that has reverted back. The UE being a non-CSG member iscapable of reverting back until it succeeds in HO, and thus will notleave from the RRC connected state.

As to whether or not the UE being a non-CSG member has successfullyperformed redirection may be judged from as to whether or not HO hascompleted at a hybrid cell in a case where a specific method ofredirection is HO. It suffices that redirection is considered to havesucceeded in the case where HO has completed and redirection isconsidered to have failed in the case where HO has not completed.Whether or not HO has completed may be judged from whether or notresources have been released in Step ST1514 of FIG. 15.

In a case where a specific method of redirection is release of RRCconnection from a hybrid cell or camping on another cell after therelease of RRC connection from the hybrid cell, the UE leaves from theRRC connected state in each case, which particularly causes no problem.Therefore, it suffices that the CSG-indicator of the SIB1 is changed(from FALSE to TRUE) when the hybrid cell starts the operation.

This enables to, when a hybrid cell is congested, solve a problem thatRRC connection cannot be always re-established in a case of an HOfailure of a UE being a non-CSG member when the UE being a non-CSGmember is redirected to another cell. Accordingly, there can be achievedeffects that the CSG member can receive benefits preferentially such ashigh-speed service and account setting at a hybrid cell, and that the UEbeing a non-CSG member can also continue communication by performing HOto another cell while keeping the RRC connected state.

First Modification of Fifth Embodiment

However, in a case where the setting for prohibiting reverting back to ahybrid cell is changed after the success of HO, a UE being a CSG membercan never access the hybrid cell unless HO succeeds. In order to preventthis, it suffices that an HO failure is regarded after a lapse of apredetermined time period, so that a UE leaves from the RRC connectedstate with the hybrid cell. The predetermined time period may be clockedwith a timer. It may be a timer for the first reception of HO controlinformation by a UE through redirection from a source cell to thesuccess of HO.

A predetermined time period is set by a source cell and is notified to aUE. Three methods of notifying the predetermined time period aredisclosed as follows.

In the first method, a cell (on a network side) makes a notification toa UE with the use of the BCCH as the broadcast information on the PBCHor PDSCH. The cell makes a notification on the PBCH using the masterinformation (MIB) or on the PDSCH using the system information (SIB).This is an excellent method in that all UEs being served thereby can benotified and that radio resources are effectively used.

In the second method, a cell determines the UE which the cell causes toperform HO and then makes a notification to the UE on a dedicatedcontrol channel (DCCH). It may be included in the measurement controlmessage notified to the UE by the cell or the mobility (HO) controlinformation notified to the UE by the cell. It suffices that thenotification is made before the first HO execution step in HO ofredirection. This enables to set an allowed time period for each UE,whereby setting can be made flexibly in accordance with the situation ofradio waves or capability of the UE to be caused to perform HO orwhether or not a UE is a CSG member.

In the third method, a static value is set as a mobile communicationsystem. The static value as a mobile communication system represents avalue known to a UE and a base station as a mobile communication system,or a value described in, for example, specifications. As a result, aradio signal does not occur between a base station (on a network side)and a UE. Accordingly, there can be achieved an effect that radioresources are effectively used. Further, the value is determined in astatic manner, whereby it is possible to achieve an effect thaterroneous reception of a radio signal is prevented.

The method disclosed in an eleventh embodiment is applicable as aspecific example of the timer. One example thereof is the method ofcausing the time period until HO success to be integral multiple of atimer for conventional HO (T304, see Non-Patent Document 9) andnotifying the UE of the integer value by the source cell. This allowsthe source cell to flexibly set the time period until HO success inconsideration of the time period until one HO failure of the UE being anon-CSG member and the allowed access time delay of the UE being a CSGmember to the hybrid cell. As this timer, it is possible to use a newtimer disclosed in the eleventh embodiment.

This prevents the situation in which a UE being a non-CSG member cannever succeed in HO and thus a UE being a CSG member can never access ahybrid cell in a congested state.

Sixth Embodiment

In a case where a hybrid cell is congested, when the CSG-indicator thatis the broadcast information of the cell is changed (from FALSE to TRUE)to redirect a UE being a non-CSG member to another cell, a time periodis spent wastefully before the UE being a non-CSG member leaves from theRRC connected state to be ready to perform the next operation in a caseof an HO failure. In order to solve this problem, returning back to thesetting of a source cell is prohibited in a case of an HO failure in thepresent embodiment. In other words, reverting back to a source cell whenHO fails is prevented.

Specifically, at least while the CSG-indicator that is the broadcastinformation of a hybrid cell operates as TRUE, returning back to thesetting of a source cell is prohibited even when HO fails in a casewhere a hybrid cell redirects (HO) the UE being a non-CSG member toanother cell. This prevents the UE being a non-CSG member that hasfailed in HO from returning to the setting of a source cell andperforming the procedure for RRC connection re-establishment. As aresult, an unnecessary procedure is eliminated, leading to an effectthat the control in an HO failure can be simplified.

Further, it suffices that in a case where the UE being a non-CSG memberthat has been redirected (HO) to another cell fails in HO to a targetcell, a procedure of leaving the RRC connection is started immediately.

FIG. 19 shows a specific example of the operation of a UE in a case ofan HO failure, which is disclosed in the present embodiment. Thedescription of the same step numbers as those of FIG. 18 in FIG. 19 isomitted. In Step ST1801, a UE detects an HO failure. In Step ST1901, theUE judges whether or not HO is one in a congested state. In a case whereHO is not one in a congested state, the UE moves to Step ST1802 andexecutes the normal procedure in an HO failure. In a case of HO in acongested state, the UE prohibits returning back to the setting of asource cell and immediately moves to Step ST1806. The UE being a non-CSGmember that has been redirected (HO) from a hybrid cell in a congestedstate corresponds to Yes in Step ST1901, which fails in RRC connectionre-establishment in Step ST1806 and immediately leaves from the RRCconnection.

As a result, even if the UE being a non-CSG member fails in HO, it canleave from RRC connection and perform the procedure of cell selectionwithout waiting the time period (T311) allowed for the normal procedureof RRC connection re-establishment. Therefore, the UE being a non-CSGmember can search for a cell on which it can camp in a short time periodwithout a delay.

Note that in a case of starting the procedure for leaving RRCconnection, not the procedure for cell selection but the procedure forcell reselection may be performed. Further, the UE being a non-CSGmember is allowed to search for a cell on which it can camp in a shorttime period without a delay.

When leaving RRC connection and then performing cell selection or cellreselection in the procedure for cell selection or cell reselection, theUE being a non-CSG member does not select a source cell. This is becauseit is an HO failure while the broadcast information CSG-indicator of thehybrid cell being a source cell operates as TRUE. The source cell is nolonger a suitable cell, and accordingly camp-on cannot be performedthereon. Therefore, the UE being a non-CSG member can immediately accessanother cell without selecting a hybrid cell in a congested state thathas been a source cell.

Seventh Embodiment

The present embodiment discloses another method for solving a problemthat in a case where a hybrid cell is congested, the UE being a non-CSGmember always cannot re-establish RRC connection in an HO failure whenthe CSG-indicator that is the broadcast information of a cell is changed(from FALSE to TRUE) and a UE being a non-CSG member is redirected toanother cell.

At least while the CSG-indicator that is the broadcast information of ahybrid cell operates as TRUE, a plurality of target cells are set in HOfrom the hybrid cell. In a case where a plurality of cells are treatedas target cells and the UE being a non-CSG member fails in HO to thefirst target cell, the UE attempts to perform HO to another target cell.This solves a problem that RRC connection cannot always bere-established in an HO failure.

A specific operation is described. FIG. 20 shows a sequence example inwhich a plurality of cells are treated as target cells when a hybridcell is in a congested state. The description of the same step numbersas those of FIG. 17 in FIG. 20 is omitted. In this example, the sourcecell is a hybrid cell. In Step ST1704, the source cell determines a UEbeing a non-CSG member in the RRC connected state which the cellredirects (HO). In Step ST2025, the source cell notifies the UE being anon-CSG member which the cell causes to perform HO of a measurementcontrol message, and in Step ST2026, the UE notifies the source cell ofa measurement report. In Step ST2001, the source cell determines aplurality of target cells based on the measurement report. As disclosedin the fourth embodiment, Step ST2025 and Step ST2026 may be omitted.

In Step ST2002, Step ST2003 and Step ST2004, the source cell that hasdetermined a plurality of target cells in Step ST2001 notifies eachtarget cell of an HO request message for the plurality of target cellsthrough the MME (or HeNBGW). On this occasion, the HO request messagenotified to the MME from the source cell may be made such that onemessage contains the information of a plurality of target cells as shownin Step ST2002 or a message is individually set for each target cell. Inthis example, a target cell A and a target cell B correspond to aplurality of target cells. In Step ST2005 and Step ST2006, each targetcell determines whether or not to allow HO based on the load conditionof the own cell, the information regarding the UE included in the HOrequest message, and the like. This example describes the case where HOis allowed. If HO is not allowed, Ack is not returned to the source cellin response to an HO request or returns Nack indicating prohibition. InStep ST2007, Step ST2008 and Step ST2009, the target cell that hasallowed HO notifies, through the MME, the source cell of the HO requestallowance message indicating that HO is allowed. On this occasion, theHO request allowance message notified to the source cell from the MMEmay be made such that one message contains the information of aplurality of target cells as shown in Step ST2009 or a message isindividually set for each target cell. This enables for the source cellto obtain the information of the plurality of target cells to which HOhas been allowed.

In Step ST2010, the source cell determines the priorities for causingthe UE to perform HO among the plurality of target cells to which HO hasbeen allowed. In Step ST2011, the source cell notifies the UE of the HOcontrol information. Not only the information regarding one target cell,but also the information regarding a plurality of target cells isincluded in the HO control information. Further, the informationregarding the priorities of the plurality of target cells is included.The priorities may be included as numerical information. For example, 1,2, 3 . . . may be affixed to each piece of target cell information in anorder from the highest one. Alternatively, the target cell with thehighest priority, the second may be notified as, for example, a primarytarget cell and a secondary target cell, respectively. As anothermethod, Step ST2011 may be notified to UE a plurality of times. Theinformation regarding one target cell may be included in one piece of HOcontrol information such that the UE is notified for the number oftimes, which is the number of the plurality of target cells. The UEfirstly performs HO to the target cell with the highest priority and,when HO fails, performs HO to the target cell with the next highestpriority.

In an HO preparation step (from Step ST2002 to Step ST2011), an HOrequest message may be notified to one target cell as in a normal HOprocedure and, in a case of an HO failure, the HO preparation step andthe following steps may be repeated, without notifying a plurality oftarget cells of an HO request message.

However, in the normal HO procedure, the UE that has received the HOcontrol information from a source cell is detached from the source cell.Accordingly, in a case where the HO preparation step is performed on anew target cell in an HO failure, the source cell has to notify the UEof the HO control information of the new target cell again. The UE isdetached on this occasion, and thus the source cell cannot notify the UEof the HO control information of the new target cell.

The above-mentioned problem can be solved by performing the HOpreparation step on a plurality of target cells, notifying the UE of theHO control information of the plurality of target cells before the UE isdetached, and repeating the HO execution step and the following step inan HO failure.

In Step ST2013 and Step ST2014, the source cell that has determined thepriorities for causing the UE to perform HO among the plurality of cellsin Step ST2010 notifies the target cell (in this case, target cell A)with the highest priority of the data required for continuingcommunication in HO and the SN status information of the PDCP relatingthereto. The data may be notified through the S-GW, not through the MME.

Meanwhile, the UE notified of the HO control information in Step ST2011is detached from the source cell in Step ST2012, and in Step ST2015,starts synchronization with the target cell (target cell A) with thehighest priority. This example describes the case of an HO failure. HOfails when, for example, synchronization has failed in Step ST2015 orthe target cell cannot receive an RRC connection reconfigurationcomplete message (Step ST2016).

In the case of an HO failure, the source cell has to notify the targetcell (in this case, target cell B) with the next highest priority of theinformation required for continuing communication in HO. Accordingly,the source cell has to recognize that the UE failed in HO to the targetcell A. Therefore, setting is made such that an HO failure is judged ifan UE context release message is not send from the target cell A or MMEduring a certain time period. The transmission/reception of a UE contextrelease message is a part of the processing for completing HO. There maybe provided a timer for clocking a certain time period. The timer may bestopped upon reception of the UE context release message. The sourcecell judges an HO failure in a case where the timer expires (StepST2017) and, in Step ST2018 and Step ST2019, notifies the target cell ofthe data required for causing the target cell B with the next highestpriority to continue communication in HO and the SN status informationof the PDCP related thereto. The data may be notified through the S-GW,not through the MME. A timer for normal HO (T304, see Non-PatentDocument 9) may be used as this timer. Alternatively, the certain timeperiod may be derived based on the set value of the timer for normal HO.For example, the certain time period may be made shorter than the valueof the timer for normal HO by a certain time period. Then, the sourcecell may notify the target cell with the next highest priority of theinformation required for HO, before the UE judges an HO failure by thenormal timer and starts synchronization with the target cell with thenext highest priority.

Meanwhile, in Step ST2020, the UE that has judged a failure in HO to thetarget cell A in Step ST2016 starts synchronization with the target cell(in this case, target cell B) with the next highest priority inaccordance with the information regarding a plurality of target cellscontained in the HO control information received from the source cell inStep ST2011. It suffices that in a case where the HO control informationreceived from the source cell in Step ST2011 contains a plurality oftarget cells, the UE is allowed to perform HO again in an HO failure orperform synchronization (Step ST2015) therefor. Alternatively, the UEmay perform HO again to the cell within the range of the receivedplurality of target cells in an HO failure. In a case of receiving thepriorities in Step ST2011, the UE may perform HO in accordance with thepriorities.

After the UE establishes synchronization with the target cell B, in StepST2021, the target cell B notifies the UE of allocation information ofuplink resources and timing advance (TA) information that istransmission timing information. In Step ST2022, the UE that hasreceived the information notifies the target cell B of an RRC connectionreconfiguration complete message. Accordingly, data communication isstarted between the UE and the target cell B. In Step ST2023, the targetcell B that has received Step ST2022 performs the processing forcompletion of HO with the source cell through the MME or S-GW that is anentity of higher layer. Along with the processing for completion of HOin Step ST2023, in Step ST2024, the source cell releases the resourcesused in control associated with the information regarding the UE.

As described above, the HO preparation step is performed on a pluralityof target cells, and the HO execution step and the following step arerepeatedly performed in a case of an HO failure. Accordingly, in an HOfailure, the UE cannot always re-establish RRC connection, but canattempt to perform HO to another target cell. Therefore, in a case wherethe hybrid cell is in a congested state, when the UE being a non-CSGmember is redirected to another cell, it is possible to solve theproblem that RRC connection cannot always be re-established in a case ofan HO failure of the UE being a non-CSG member. This achieves an effectthat the CSG member is allowed to preferentially receive the benefitssuch as high-speed service and the account setting at a hybrid cell andthe UE being a non-CSG member also becomes able to perform HO to anothercell and continue communication while continuing an RRC connected state.

If HO fails to all of a plurality of target cells, the method disclosedin the sixth embodiment may be applied. It suffices that in the casewhere HO fails in the congested state of the source cell, the UE doesnot return to the setting of a source cell but immediately leaves fromthe RRC connected state. This enables, even when a UE being a non-CSGmember fails in HO to all target cells, the UE to search for a cell onwhich it can camp in a short time period without a delay.

At least while the CSG-indicator that is the broadcast information of ahybrid cell operates as TRUE, a maximum value may be provided to thenumber of target cells in allowing that the target cells in HO from thehybrid cell are treated as a plurality of cells. A maximum value may beprovided in determination of a plurality of target cells in Step ST2001,or a maximum value may be provided in determination of the priorities ofthe target cells in Step ST2010. Alternatively, a maximum value of thetarget cell that performs the concerned HO may be provided such that theUE performs HO to the target cell within the maximum value. A maximumvalue may be determined in advance or, in the case where it is used bythe UE, may be notified to the UE from a source cell or from the corenetwork side (MME, HeNBGW) through the source cell. As the notificationmethod, it may be notified to the UEs being served by the source cell ina broadcast manner using the broadcast information or may be dedicatedlynotified to the UE. In a case where the UE is notified dedicatedly, amaximum value may be contained in the HO control information to benotified.

Setting of a maximum value enables to limit an amount of the informationrequired to be notified to the target cell or UE by the source cell or asignaling amount of a message. In addition, it is possible to avoid acontrol delay caused by complicated operation as a system or congestionof signaling between a large number of cells and MMEs, HeNBGWs or S-GWs.

Eighth Embodiment

The seventh embodiment has disclosed, as an example, the method ofsimultaneously making an HO request to a plurality of target cells whenthe HO preparation step is performed on the plurality of target cells.The present embodiment discloses the method of making HO requests on aplurality of target cells in a serial manner.

FIG. 21 shows a sequence example in a case where HO requests areserially made on a plurality of target cells, which shows a new processfrom Step ST2001 to Step ST2010 that is a different operation from thatof FIG. 20 showing a sequence of entire HO. The source cell is a hybridcell. An i-th target cell is represented as a target cell #1.

In Step ST2101, a source cell determines a plurality of target cells. InStep ST2102, the source cell determines the priorities of the targetcells determined in Step ST2102. In Step ST2103, i is replaced by 0, andin Step ST2104, i=i+1. In Step ST2105, the source cell makes an HOrequest to the target cell with the i-th priority. In Step ST2106 andStep ST2107, the source cell notifies the target cell #i of the HOrequest through the MME. The target cell #i judges as to whether or notallow HO to the UE (Step ST2108) and, in Step ST2109 and Step ST2110,notifies the source cell of an HO request allowance/prohibition messagethrough the MME. The source cell that has received the HO requestallowance/prohibition message judges whether or not the plurality oftarget cells determined in Step ST2101 have been all notified of the HOrequest. In the case where they have not been notified, the source cellreturns to Step ST2104 and repeats the process up to Step ST2110 on thetarget cell with the next highest priority. In a case where the targetcells are all notified of an HO request in Step ST2111, the source cellmoves to Step ST2112 and again determines the priorities of the targetcells that have received the HO request allowance message.

It has been described here that the HO preparation step from Step ST2105to Step ST2110 is sequentially performed, and the HO execution step andHO completion step thereafter are performed sequentially as well.

Accordingly, it suffices that the source cell signals an HO requestmessage as required. This reduces an amount of signaling performedsimultaneously, and thus the congestion of signaling by means of aninterface among the cell and MME and HeNBGW, whereby it is possible toreduce signaling transmission/reception errors. The erroneous receptionof an HO request allowance/prohibition message can be reduced at thesource cell.

First Modification of Eighth Embodiment

In a case where HO requests are serially made for a plurality of targetcells, a desired number of target cells may be set.

FIG. 22 shows a sequence example in a case where a desired number oftarget cells is set. The description of the same numbers as those ofFIG. 21 in FIG. 22 is omitted. In Step ST2201, the source cell countsthe number of the target cells that have received an HO requestallowance message and judges whether or not the desired number of targetcells is satisfied. In a case where it is not satisfied, the source cellreturns to Step ST2104 and repeats the HO request again to the targetcell with the second next highest priority. In a case where the desirednumber of target cells is satisfied in Step ST2201, the source cellmoves to Step ST2112.

Accordingly, it suffices that the source cell signals an HO requestmessage only to the minimum required number of target cells. Thiseliminates wasteful signaling, which makes it possible to stabilize theoperation as a system.

As another method, in a case where HO requests are serially made to aplurality of target cells, the target cells that have received the HOrequest allowance message in a certain time interval may be treated astarget cells. There may be provided a timer that clocks a certain timeinterval. The target cells that have received the HO request allowancemessage in the time interval are treated as target cells, so that thesource cell determines the priorities of the target cells notified tothe UE in Step ST2112 again.

As a specific example, with reference to FIG. 22, i is set to 0 in StepST2103 and a timer that clocks the time interval is started, so that theprocessing in Step ST2201 is judged based on whether or not the timerhas expired. It suffices that the source cell returns to Step ST2104 ina case where the timer has not expired and moves to Step ST2112 in acase where the timer has expired.

This enables to limit the time period required for the HO preparationstep, whereby it is possible to limit the time period of disconnectionof a conversation of a UE being a non-CSG member that is redirected (HO)from the hybrid cell in a congested state to another cell. In addition,it is possible to reduce the time delay until the UE being a CSG memberthat newly performs RRC connection with the hybrid cell becomes able tocommunicate.

Note that those methods may be used in combination. Alternatively, themethod disclosed in the first modification of the eighth embodiment isapplicable also to a case of making HO requests to a plurality of targetcells non-serially, which has been described in the seventh embodiment.

Ninth Embodiment

In the seventh and eighth embodiments, at least while the CSG-indicatorthat is the broadcast information of a hybrid cell operates as TRUE,target cells in HO from the hybrid cell are allowed to be a plurality ofcells. The method of performing the HO preparation step on a pluralityof target cells and repeating the HO execution step and the followingstep in a case of an HO failure is disclosed as a specific operationexample.

As another specific example, the present embodiment discloses, of the HOpreparation step and the HO execution step, the method of performing, ona plurality of target cells, the process up to the notification of thedata required for continuing communication in HO by target cells and theSN status information of the PDCP related thereto, and repeating thefollowing step.

FIG. 23 shows a sequence example in which the process up to thenotification of the data required for continuing communication and theSN status information of the PDCP related thereto is performed on aplurality of target cells. The source cell is a hybrid cell. Thedescription of the same numbers as those of FIG. 20 in FIG. 23 isomitted. With reference to FIG. 23, the source cell determines thepriorities of a plurality of target cells in Step ST2010 and the HOcontrol information is notified to a UE being a non-CSG member in StepST2011, which are identical to FIG. 20. In Step ST2301, Step ST2302 andStep ST2303, the source cell notifies a plurality of target cells of thedata required for continuing communication in HO and the SN statusinformation of the PDCP related thereto. The data may be notifiedthrough the S-GW, not through the MME. It suffices that the plurality oftarget cells are identical to a plurality of target cells contained inthe HO control information notified to the UE in Step ST2011. In thisexample, they are a target cell A and a target cell B. The data requiredfor continuing communication in HO, which is notified to the S-GW fromthe source cell, may be made such that the information of a plurality oftarget cells is included in one message as shown in Step ST2301 or amessage is provided dedicatedly for each target cell. Further, the SNstatus information of the PDCP related to the data required forcontinuing communication in HO, which is notified from the source cellto the MME or HeNBGW, may be made such that the information of aplurality of target cells is included in one message as shown in StepST2301 or a message is set dedicatedly for each target cell.

This enables to notify the all cells that are target cells not only ofthe context information related to the UE notified from the source cellin Step ST2002, Step ST2003 and Step ST2004 but also of the datarequired for continuing communication in HO and the SN statusinformation of the PDCP related thereto. Accordingly, even if the UEbeing a non-CSG member fails in HO to a target cell with the highestpriority and performs HO to the target cell with the next highestpriority, the target cell possesses the information required for HO,which enables HO of the non-CSG member.

Alternatively, in this case, the UE may determine the priorities oftarget cells. Even if the UE selects the next target cell when HO fails,the cell to be a target candidate has already possessed the informationrequired for HO, whereby it is possible for the UE to perform HO. As aresult of the UE determining the priorities of target cells, the sourcecell notifies the information of a plurality of target cells in StepST2011 but is not required to notify the information of the priorities.Therefore, an amount of information can be reduced. Further, theprocessing of Step ST2017 shown in FIG. 20 is not required. The sourcecell has already notified all of the target cells of the informationrequired for HO, and accordingly in a case where a UE fails in HO, isnot required to send the information required for HO to the cell withthe next highest priority. As a result, the source cell does not need torecognize an HO failure between a UE and a target cell. Therefore, theprocessing in Step ST2017 is not required. This enables to simplify theHO processing at the source cell. Further, the UE determines thepriorities of target cells, which achieves an effect that a target cellthat is highly likely to be connected to the UE can be selected.Further, the source cell does not need to notify, in each HO failure,the target cell of the data required for continuing communication in HOand the SN status information of the PDCP related thereto, whichachieves an effect that a time period until HO is completed can bereduced.

The method disclosed in the present embodiment does not always prohibitRRC connection re-establishment in an HO failure but enables to attemptHO to another target cell. This solves the problem that, in a case wherea hybrid cell is congested, RRC connection re-establishment is alwaysprohibited in an HO failure of the UE being a non-CSG member when the UEbeing a non-CSG member is redirected to another cell. Therefore, the CSGmember can preferentially receive benefits such as high-speed service ata hybrid cell and the account setting. In addition, there can beachieved an effect that a UE being a non-CSG member can also perform HOto another cell and continue communication while continuing the RRCconnected state.

The methods disclosed in the seventh embodiment to the ninth embodimentare applicable at least while the CSG-indicator that is the broadcastinformation of a hybrid cell operates as TRUE, which is not limitedthereto. In addition, those methods may be applied to the HO procedurein a case where HO destinations are a plurality of target cells. Thisenables to reduce a possibility that HO may fail.

Tenth Embodiment

In the present embodiment, the source cell (hybrid cell in a congestedstate) notifies the UE to be a redirection target of the redirectionfrom the hybrid cell in the congested state. This notification isdesirably performed before the HO execution step.

As a specific example of the method, the source cell determines a UEbeing a non-CSG member in the RRC connected state which the cell causesto perform HO in Step ST1602, which is disclosed in FIG. 16, and thenmakes a notification to the UE using the dedicated control channel(DCCH). This notification is desirably performed before the HO executionstep.

The notification may be included in the measurement control messagenotified to the UE by the source cell in Step ST1501. This enables asource cell or the UE to distinguish the measurement in HO by theredirection from a hybrid cell in a congested state from the measurementin normal HO, which allows the measurement method, for example, thecriteria of a report or a threshold of an event to vary between twotypes of HO.

As another method, the notification may be included in the measurementHO control information in Step ST1507. Similarly, this enables a sourcecell or the UE to distinguish HO by the redirection from a hybrid cellin a congested state from normal HO. Further, it is applicable to a casewhere, for example, measurement control is omitted.

As a specific method of indicating the redirection from a hybrid cell ina congested state, 1 bit of information may be used. For example, it isconceivable that normal HO is applied in a case of “0” and HO by theredirection from a hybrid cell in a congested state is applied in a caseof “1”.

The source cell notifies the UE to be a redirection target of theredirection from a hybrid cell in a congested state, which enables touse the notification in the judgment performed by the UE as to whetheror not HO is one in the state in which a source cell is congested, whichis disclosed in the sixth embodiment (Step ST1901 of FIG. 19). When theUE fails in HO, it is possible to use the notification in the judgmentas to whether to return to the setting of a source cell (reverting backis performed) or not to return to the setting of a source cell(reverting back is not performed). Alternatively, the notification maybe used as the judgment index whether or not the UE redirected (HO) tothe hybrid cell in a congested state performs HO again in an HO failure.For example, in a case where the maximum number of target cells differsbetween normal HO and HO by redirection, the number of target cells towhich HO is tried again may be changed based on the informationindicating the redirection from the hybrid cell in the congested state.

The method disclosed in the present embodiment enables a UE to be aredirection target to explicitly receive the indication that theredirection is one from a hybrid cell in a congested state, wherebymalfunctions such as erroneous adoption of another HO method unlikely tooccur. Accordingly, as a system, it is possible to stabilize anoperation also in a case of using the method of redirecting to anothercell at a hybrid cell.

Eleventh Embodiment

In the present embodiment, a timer for clocking, by a UE, the allowedtime period for HO in which a plurality of target cells are set is newlyprovided separately from the timer for clocking the allowed time periodfor conventional HO in which a single target sell is set.

The timer for normal HO (T304, see Non-Patent Document 9) clocks thetime period of a UE from receiving the HO control information from asource cell to succeeding in HO, that is, the time period until the UEtransmits an RRC connection reconfiguration complete message to a targetcell. In other words, this timer is a timer for HO to one target cell,which serves as a timer for judging whether or not HO to one target cellfails. In a case where HO is enabled to a plurality of target cells,this timer is used for HO to each target cell. That is, in a case whereHO is enabled for a plurality of target cells, the allowed time periodfor a series of HO cannot be set. The allowed time period for a seriesof HO determines a time delay until a UE that is to receive a service ata source cell starts receiving the service or the communicationinterruption time of a UE performing HO. This means the importance indetermining the operation of a system.

Therefore, in the present embodiment, the allowed time period (timer)for HO by a UE is newly provided separately from the allowed time period(timer) for conventional HO. As a specific example, there is providedthe allowed time period (timer) of a UE from receiving the HO controlinformation from a source cell to succeeding in a series of HO.

In a case where a UE fails in HO and repeatedly performs HO to aplurality of target cells, a series of HO is judged to have succeeded ifthe RRC connection reconfiguration complete message has been transmittedto any of target cells within the timer. However, in a case where theRRC connection reconfiguration complete message cannot be transmitted toany of target cells within the allowed time period, a series of HO isregarded as a failure, and the processing in an HO failure is performed.As the processing in an HO failure, it can be used in judgment as towhether or not HO is one performed by the UE in a state in which asource cell is congested, which is disclosed in the sixth embodiment(Step ST1901 of FIG. 19). This limits the allowed time period for aseries of HO, whereby it is possible to limit the time delay until theUE that is to receive a service at a source cell starts receiving theservice or the communication interruption time of a UE performing HO.

The allowed time period for a series of HO disclosed in the presentembodiment and the conventional HO allowed time period may be used incombination. In a case where HO is enabled for a plurality of targetcells, the conventional HO allowed time period may be used for HO toeach target cell and the allowed time period for a series of HO may beused for a series of HO. The use of the timer for HO to each target cellallows the UE to recognize an HO failure to the target cell and thenperform HO to a target cell with the next highest priority.

The allowed time period for conventional HO may be treated as theallowed time period for a series of HO, and the newly provided allowedtime period for HO may be treated as the allowed time period for HO toeach target cell. In any case, the above-mentioned effect can beachieved.

Three methods of notifying the allowed time period (timer) for a seriesof HO are disclosed below. In the first method, a cell (on a networkside) makes a notification to a UE with the use of the BCCH as thebroadcast information on the PBCH or PDSCH. The cell makes anotification on the PBCH using the master information (MIB) or on thePDSCH using the system information (SIB). This is an excellent method inthat all UEs being served thereby can be notified and that radioresources are effectively used.

In the second method, a cell determines the UE which the cell causes toperform HO and then makes a notification to the UE on a dedicatedcontrol channel (DCCH). The notification is performed before the HOexecution step. It may be included in the measurement control messagenotified to the UE by the cell or the mobility (HO) control informationnotified to the UE by the cell. This enables to set an allowed timeperiod for each UE, whereby setting can be made flexibly in accordancewith the situation of radio waves or capability of the UE to be causedto perform HO or whether or not a UE is a CSG member.

In the third method, a static value is set as a mobile communicationsystem. The static value as a mobile communication system represents avalue known to a UE and a base station as a mobile communication system,or a value described in, for example, specifications. As a result, aradio signal does not occur between a base station (on a network side)and a UE. Accordingly, there can be achieved an effect that radioresources are effectively used. Further, the value is determined in astatic manner, whereby it is possible to achieve an effect thaterroneous reception of a radio signal is prevented.

As another specific example of the method of newly providing the allowedtime period (timer) for HO in a UE separately from the allowed timeperiod (timer) for conventional HO, the allowed time period for a seriesof HO is caused to be integral multiple of the allowed time period forconventional HO. For example, when Ttotal represents the timer for aseries of HO and Tsingle represents the timer for conventional HO,Ttotal=Tsingle×n (n is a positive integer). The method described aboveis applicable as the method of notifying a value of n. As a result,compared with the case of newly providing a detailed allowed timeperiod, it is possible to reduce the amount of information because n isa positive integer. Alternatively, n may be a maximum value of a targetcell. As to the maximum value of a target cell, the method disclosed inthe seventh embodiment is applicable. In a case where the UE is notifiedof the maximum value of a target cell from the source cell, this valueof n may not be notified. This further reduces an amount of information.

In the specific example disclosed in the present embodiment, newlyprovided HO allowed time period is used as the allowed time period for aseries of HO, with the conventional HO allowed time period as theallowed time period for HO to each target cell. Not limited to theabove, the newly provided allowed time period for HO may be treated asthe allowed time period for HO to each target cell, with the allowedtime period for conventional HO as the allowed time period for a seriesof HO. In any case, the above-mentioned effect can be achieved.

The present embodiment is generally applicable to the case where aplurality of cells are treated as target cells in HO, not limited to thecase where a plurality of cells are treated as target cells in HO from ahybrid cell when the hybrid cell is congested.

In deleting CSG registration of a UE, HO led by a cell or network may beperformed, and then, the methods disclosed in the fourth embodiment tothe eleventh embodiment may be applied to the HO. In a case where theCSG registration of the UE is deleted, a cell belonging to the CSG is nolonger a suitable cell. In a case where a UE is in an RRC connectedstate with the cell belonging to the same CSG to which the UE belongs,when HO led by a cell or network is performed in deletion of the CSGregistration of the UE, it is possible to solve a problem occurring dueto a fact that the source cell is no longer a suitable cell.

In expiration of the CSG registration period of a temporary member UE ofthe CSG, HO led by a cell or network may be performed, and the methodsdisclosed in the fourth embodiment to the eleventh embodiment may beapplied to the HO. In a case where the CSG registration period of thetemporary member UE expires, it is possible to solve a problem similarto the above, which occurs due to a fact that the cell belonging to theCSG is no longer a suitable cell.

In power-off of the HeNB, HO led by a cell or network may be performed,and the methods disclosed in the fourth embodiment to the eleventhembodiment may be performed on the HO. In the case where the power ofthe HeNB is turned off, access to the cell (HeNB) becomes impossible,whereby it is possible to solve a problem, which is caused as a resultof the above, similar to the above-mentioned problem.

The present invention does not particularly describe a frequency carrierof a system, which may be intra-frequency cell reselection, cellselection or handover, or may be inter-frequency cell reselection, sellselection or handover. For example, the present invention is alsoapplicable to the case where a CSG cell is operated on a dedicatedfrequency carrier different from that of a non-CSG cell.

The present invention has individually described the first embodiment tothe eleventh embodiment, which may be used in combination.

It is possible to flexibly deploy a hybrid cell in a system or providevarious services, as well as to favor, at a hybrid cell, the access ofCSG members belonging to the same CSG as the hybrid cell belongs to thatmake access in a closed access mode over the access of non-CSG membersthat make access in an open access mode for providing benefits inservice and account setting.

While the LTE system (E-UTRAN) is mainly described in the presentinvention, the present invention is applicable to the W-CDMA system(UTRAN, UMTS) and LTE-Advanced. Further, the present invention isapplicable to a mobile communication system in which a closed subscribergroup (CSG) is introduced, a communication system in which an operatoridentifies subscribers and the identified subscribers are allowed accessas in the CSG, and a communication system in which a cell having asmaller cell radius compared with a normal cell is introduced as in thecase of HeNB.

1-17. (canceled)
 18. A mobile communication system hybridly allowing, ina case where an access group consisting of one or more user equipmentsand one or more base stations is registered, the base station includedin said access group to have access in a closed mode from the userequipment included in the same access group and access in an open modefrom a user equipment that is not included in the same access group,wherein in a congested state, the user equipment in the open mode isredirected from a hybrid base station that is hybridly allowed theaccess in said closed mode and the access in said open mode to anotherbase station.
 19. The mobile communication system according to claim 18,wherein in a case where the user equipment in the closed mode requestsconnection to said hybrid base station, the connection between the userequipment in said closed mode and said hybrid base station is completedafter redirecting the user equipment in the open mode from said hybridbase station to another base station.
 20. The mobile communicationsystem according to claim 18, wherein in a case where the user equipmentin the closed mode requests connection to said hybrid base station, theuser equipment in the open mode is redirected from said hybrid basestation to another base station after completing the connection betweenthe user equipment in said closed mode and said hybrid base station. 21.The mobile communication system according to claim 18, wherein in a casewhere the user equipment in the open mode is redirected from said hybridbase station to another base station through handover, a setting changeto prohibit reverting back to said hybrid base station is executed afterthe handover succeeds.
 22. The mobile communication system according toclaim 18, wherein in a case where the user equipment in the open mode isredirected from said hybrid base station to another base station throughhandover, the connection between the user equipment in said open modeand said hybrid base station is released after a lapse of apredetermined time period.
 23. The mobile communication system accordingto claim 18, wherein reverting back to said hybrid base station isprohibited in a case where redirection from said hybrid base station toanother base station fails.
 24. The mobile communication systemaccording to claim 18, wherein a plurality of target base stations forredirection from said hybrid base station are set.
 25. The mobilecommunication system according to claim 24, wherein in a case where theuser equipment in the open mode is redirected from said hybrid basestation to another base station through handover, among all handoversteps including a handover preparation step, a handover execution stepand a handover completion step, said handover preparation step isnon-serially performed on a plurality of base stations and said handoverexecution step and said handover completion step are sequentiallyperformed on the plurality of base stations until the handover succeeds.26. The mobile communication system according to claim 24, wherein in acase where said hybrid base station redirects the user equipment in theopen mode to another base station through handover, all handover stepsincluding a handover preparation step, a handover execution step and ahandover completion step are sequentially performed on a plurality ofbase stations until the handover succeeds.
 27. The mobile communicationsystem according to claim 18, wherein said hybrid base station notifiesthe user equipment in the open mode of redirection to another basestation.
 28. The mobile communication system according to claim 24,wherein in a case where the user equipment in the open mode isredirected from said hybrid base station to another base station throughhandover, a time period for defining a failure of a series of handoverto a plurality of target base stations is set, and a handover failure isregarded after a lapse of the time period.